she doesnt know what steam is either

^Well, without impulse you won't be able to update any of your games, so even with Trinity you will be unable to play multiplayer after the next update. The easiest and cheapest way to get it is to convince your mom (if she won't believe you maybe a somewhat tech or game literate friend she trusts will vouch for you?). Otherwise I think the trinity version comes with Entrenchment and Diplomacy on a disk, though you are essentially buying the originally Sins of a Solar Empire again, so I would do this as a last resort.

I think Stardock might accept mailed-in checks but you'll have to ask someone at Stardock.  If you have a checking account I guess maybe you could send them a check or if not get a money order and mail it to them.  I'm sure someone from Stardock will comment about this soon.