Repeat, Sedna is NOT a healer. Demigod is classless, and unlike games like diablo 2 etc where some builds just cannot hold their muster Demigod is incredibly well balanced and well thought out.
Heal isn't a come all save all ability, it has high cool down, fairly high mana usage, and a cast timer which allows for easier interruption. Plus, if you are running and there is more than one guy on your tail, it is usually fatal to use as it just allows the other demigods to catch up and that 1500 health is out the window pretty fast.
So to that end, here is a list of Sedna builds I have, all of which do not necessarily need heal. I am so sick and tired of being berated TIME AND TIME again for not being a healer and others rage quitting saying "our healer doesn't heal".
The main reason I lose if I take a non heal build is my team's moral seems to sink through the floor. Because they don't understand. This is not EQ. You can actually win with three thief like characters, vs. three healers or three tanks, or whatever. This isn't EQ. Classes don't matter, each demigod is just another approach to an end and classless in their own right.
One thing of note though, Sedna innately boosts healing of all priests, and includes healers you buy at the item store. With her ability to increase attack speed of minions to boot, they can add a sizable dps to your arsenal. Plus, the priests you buy heal without taking time, on the run, and use zero mana. I highly recommend them for any sedna build. But that isn't to say it is necessary or essential. You can, and many do, win with no general priests. The main disadvantage is you can't control when they heal. They heal about every 9 seconds, in an area effect so sometimes this means your allies who really needed it get left out. It is micromanagable though.
Ok, build time.
Legend:
> ability on left takes precedence
= ability on left and right are equivalent for build
First line is primary abilities
Second line is secondary
All other talents tertiary
Standard Pounce + Heal Build (PH Sedna)
Heal > Pounce
Healing Wind = Magnificent Presence = Silence = Inner Grace
Common Items (for beginning)
Priest Idol
Run Favored Item (+15%)
Vlemish Faceguard
Boots of Speed or Assassins Footguard
Hauberk of Life
Advantages:
Good Spike and Anti Spike damage
Heal Level 3 can be life saving because it can clear debuffs (i.e. save ally from run speed debuffs etc)
Aid allies survivability
Pounce can stun, ability to take and give life with pounce and heal in your arsenal
Disadvantages:
Low HP due to investment in mana items. Or conversely many trips to town, etc. Sedna already has a low hp. So this can be devastating in a spike damage situation where you cannot get heal off in time.
Long term survivability hurt by dependence on mana and non-maxed or late game ability regens
Running away isn't as good as you're slower for your level than other builds (due to lack of Inner Grace early on)
Chasing down other enemies and being truly offensive isn't nearly as strong as other builds
Effective HP (from regen over time) in engaged battles isn't as
Long engaged battles wear mana thing quick.
Don't always get to use pounce because you are low on mana and pounce is far less mana efficient for hp/mp difference. Too heal will often be usable and pounce will not during low mp.
In an even match, you are the one usually running away due to defensive nature and dependence on mp.
Not an asset for map control on your lonesome, need allies to have true push power. Again, you are usually running in this situation. You CAN sometimes outlast and make other demi's run away but it isn't consistent (against even or better ranked players, anyhow but we're talking of build strengths here not players)
Low Area Damage
Dissertation:
You are able to deal damage, interrupt other demigods abilities (which can save a ton of health or keep them from getting a defensive ability off, such as heal), you are able to add a ton of survivability for spike damage to your character (long term isn't as affected however). Take healing wind to add more long term survivability and save mp on heals. Take Magnificent presence to burn through your abilities even sooner and support your allies in being able to use their abilities sooner. Take silence to add more survivability or use for running enemies to keep them from using any getting away abilities, or use to cover your own arse as you escape so there aren't any stuns locks going on etc. Use inner grace to add survivability, easier chasing down of other enemies, get to allies quicker for supporting and/or simply running away.
Constantly out of mana, so you are constantly investing in mana items. After a certain point you are pretty good on mana, but it is a game maker early game. Also highly ability dependent so stuns, interrupts and ability delays are exceedingly difficult to cope with.
Overall:
The standard/favored Sedna build. And it works well, and people know that. Be aware of its weaknesses however. Sedna's low hp is somewhat countered for with 1500 extra hp heals. However, you cannot always rely on that as you can on hp items and gear. Paired with Priest Idols, you are very hard to take down (in the short term) with anything but extreme coordinated spike damage and/or stuns. You can add a fair share of damage yourself to a spike damage take down, but you cannot always chase a low hp enemy down when other builds might. Running away is also harder in a ton of situations.
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Minion (Minion Sedna)
Yetis > Magnificent Presence > Healing Wind (optional)
Heal = Pounce = Silence = Inner Grace
Common Items (for beginning)
+ Bishops (top tier REQUIRED)
+ Siege Demolishers (top tier REQUIRED)
+ Minotaurs (top tier REQUIRED)
+ Hauberk of Life (VERY good for this build as adds minion hp as well)
Gladiator gloves (Descent, +4 doesn't sound like a lot till you consider you have 10 minions, so that's adding something around 40 dmg per cycle.)
Run Favored Item (+15%)
Vlemish Faceguard
Boots of Speed or Assassins Footguard
Advantages
Has more staying power than the Light Tower Rook. Seriously.
Siege wrecker
You literally push others around the map.
You are safe in your ring of minions
Running away you're still doing most the damage you were (grins)
You can send minions behind towers to finish others off in ways another build never could
Mine clearing was never as easy as this
Rook Towers are cake walks
UB and other high damage characters end up running quickly.
GREAT Auto attack DPS (each purchased minion adding about 60 dmg at some point, and yetis doing some aoe damage)
If they concentrate on you, you can run around while your minions hit on them and if they try to take your minions on they will lose so 
They can take on Waves of fully upgraded giants, catapults, angels, priests and soldiers all on their lonesome. I once held a base against 2-3 oncoming waves at once with this build while unsupported by teammates. Granted if a demigod comes into the mix things can get gruesome but I still manage to usually push them away WHILE gaining xp from minions and holding them off.
You render Unclean Beast and other High Damage / Weaker defense characters (if same level, play level etc) pretty useless on the open map without support since they can only run. Fear the Beast running in spitting and then stunning then coming in for ko, it is not bullet proof but you have a big advantage.
You kinda, almost have an AoE type build and can run through pretty much every other minion build I have seen. Minion builds aren't common however, especially ones where they buy EVERY minion available. Erebus can compete however, so watch out. The advantage you have over EVERY other minion build is you are completely summon based. They have to kill minions to rebuild their army. You don't. So you get your map pushing control again as soon as an Erebus encounter is done.. for a bit of time 
Disadvantages
Minions will not die to one AoE attack after they are fully buffed but two or three..
If all your minions die you are out quite a bit of mana, it almost necessitates a trip to the crystal (at least your minions can fight on in the mean time however)
Auto Attack DPS can be hugely countered by a ton of armor, a ton of hp is not as effective.
You can push others around the map but you can't kill them under most circumstances. Even though your minions inherit your run speed buffs since it isn't a focus many can outrun you.
AoE Stuns disable your minions (Erebus, Torch Bearer's Freeze) and are probably the biggest concern. If you see it just run till they are up and moving again.
You can't be front line a lot as most your money went to minions. So a lot of time you aren't even engaging for extra auto attack damage...
Micro managing the less than stellar AI can be a pain every now and again.
Over dependence on run speed, maybe?
Dissertation:
Sedna minion builds are pretty much all or nothing. Your Yetis do NOT do damage. At top level four of them can take down a tower by themselves if it isn't TOO upgraded. So yeah, they are weak. On their own. For damage. That is why you got all the other minions as support. Yetis have a sick ton of hp. There's four of them later too. Collectively they are a cheaper cast than your other minions as well. Really, they soak damage. While this is good against AI's, computer player's know different. Still, they seem to soak a ton of damage from them as well. And though their damage on their own can be some ignored, in your entire set up it pushes everything over the edge to make yourself proclaimed army a force to be reckoned with.
For secondary abilities, if you want the ability to finish off those running targets, try pounce. If you want to never die behind your meat wall and be able to heal allies too, take heal. Heal level 3 and on is useful to clear run debuffs and dps effects on you. If you want to be mobile and allow your minions to be able to chase down behind enemy lines more, Inner Grace (NOTE inner grace does not seem to pass on to minion run speed, pending further testing). If you want to disable enemies and watch them scream as your minions rip them apart, try out silence.
Overall:
A highly under-rated build that has the most staying power I have seen in the game. Want a flag or a point on the map that the enemy lines are going to have a terrifically hard time getting through? Sick a minion build Sedna on em. Do not expect a ton of glory however, as you are not going to get many kills, maybe a ton of assists however. Flag Capture count should be high. You are spending a ton on items too however, so don't look to be the citadel upgrade king, and without many kills don't look to be a gold king. Unlike other builds however, you CAN expect to have high creature kill counts. And you can of course do the most siege damage in a game and can even in some instances take the damage given cake. It is harder then say, a torch bearer, but is doable. Many of these things you cannot see in a PH Sedna build.
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Hunter (Hunter Sedna build) [AKA Aura build with pounce]
Pounce > Magnificent Presence > Inner Grace > Healing Wind
Heal = Silence = Counter Heal
Common Items (for beginning)
Priest Idol (I pretty much list this as a requirement, but the 2700 for Bishops definitely can be spent elsewhere to everyone's benefit, but it will make it harder to live longer, nothing is better than toe to toeing with a beast two levels higher and watching him fall over. It works)
Run Favored Item (+15%)
Vlemish Faceguard
Boots of Speed or Assassins Footguard
Duelists Cuirass
Nature's Reckoning (Since Sedna is a fast attacker any proc on hit abilities can be fairly beneficial, this is great for clearing hordes of minions AND adding about 15% chance for 2x attack even late levels for a single target/demigod)
Advantages
Most aggressive sedna build I've found in the game
GREAT spike damage
GREAT movement speed
GREAT regen adds to long term survivability and a much greater effective hp in engaged battles
Best at retreat
Best at hunting running characters down
Very good at getting other characters to run.
Pretty good map control tactics since you are making them run more often than not
Best Sedna build for killing. I have out killed in several instances Regulas, Unclean Beast, etc who are focused on these things.
Great run speed + High Regen = High survivability
Around others, you are a force to be reckoned with (Group regen, Group ability reuse time reduced + Vlemish if you got it)
Rather Offensive, which means you control the map more, kill other demigods more, and that ends you with more gold so you can get more items, etc.
Disadvantages
Investment needs in hp gear to resist damage spike kills
Not as much staying power as minion build due to reliance on mp costs of pounce over and over (at higher levels every 4 secs)
Rewards are greater, so are risks
No ability to help other demigods that overextended themselves (at least early game)
Over dependence on run speed, if there are other run speed addicts you have to spend a ton on run speed items to keep out of their way and/or chase them down
Dissertation
This builds greatest weakness is coordinated spike damage, between more than one demigod and run debuffing. In even engaged battles with an equal leveled foe, you will have priority however. So, pretty much the only thing that kills you is the thing that kills any demigod (coordinated spike damage), since your regen and run speed is through the roof you do not have to worry AS much about being chased down and killed, in 2 vs. 1 though it is and always will be 2 vs. 1. Just be battle aware if there's two coming, and you are alone, do something else and wait for allies. This goes for every build, but is especially necessary here since you do not want to waste mana on engaging when it won't be as beneficial and if they stun lock you, you die anyway and if they speed debuff you, you are in for a world of hurt without heal 3 or way better run speed than the other guy. However, due to the fact you sac heal 3, you are faster, regen better, and can use pounce a lot more often and make other demigods run pretty often.
Secondary Abilities: Silence really helps you finish off enemies or get away but beware of its insane mp cost. Counter heal is GREAT and will help you kill other demigods all the more. They will expect a heal from minions, or a bought minion and BAM won't receive it and perish
Heal is good if your allies are over extending themselves a ton, or you need to be able to clear debuffs on such things as run speed decreaser or dps, or otherwise.
Overall
This my favorite build. It adds a ton of spice to the game, as said the Rewards are greater, so are the risks. If you're winning your teammates are amazed at your kill ratio, everything. The bummer is if you are not winning they complain and blame your build for it rather than the fact they run when it's 2 against 1 in your favor, or they consistently go 2 against 1 not in favor, or they use their abilities at times way off from yours so you cannot coordinate spike damage killing, or they sat in town too long, or they under leveled because they have been feeding the enemy or have been concentrating on only killing the enemy instead of getting minions or they cannot hold a flag because the other players are simply better than them. All those things and even more have nothing to do with the Sedna build and everything to do with the player. So please, just try and coordinate and please stop seeing Sedna as a "Healer". Cause she's not, she's a demigod which so happens to have an healing ability which is entirely optional.
Feel free to add other sedna builds, give your opinion on mine, etc. Regards.