My original question aside. I decided not to have this NPC be a servant of the balance, here's why:
Her brother is a Life Stealer (Warrior Priest, Chardros) and to acheive the Maker of Knots rank, he has been sent on a mission to kill a "traitor" to the Cult of Chardros (he met the other prerequisites for the rank early on, but I told him he had to complete his mission. This isn't D&D, you have to earn this stuff, not just have the numbers to qualify).
He has just found out that the traitor is his older sister. I was originally going to have her renounce Chaos, and Chardros in particular, for the Balance, but then I thought it would show the fickle nature of the Chaos Lords better if she venerated Chaos generally. Her "treachery" being that she hasn't entered into a specific pact with Chardros as did the rest of the family.
He will have to roll either his pact skill, or his passion - love family, to determine whether or not he tries to kill her. His pact skill is in the low 80's and his passion will be probably 50 or less. Which way he should roll? Any suggestions? I'm thinking a fail on his pact skill spares her.
I do have another question though: Could the Rune of Sleep be inscribed on to the inside of a goblet or similar, effectively making any liquid drunk from it a sleeping potion?
When I get home I'll post her stat block.