Become a Designer in Satisfashion

If she drives you so insane, why do you let her *and* her husband (and obviously a child) live with you for free? I would tell her to start paying rent or get out. Out of the two of them (especially if your parents babysit for her) there is no reason why she shouldn't be able to pay for half the rent, utilities, etc.

Or, if there is a reason that she is living with you (obviously, there is no way that I know all the facts), confront her about her actions and have her explain herself. Communication can do wonders for a relationship.