Moral Dilemma!

[GLJordan]

set it up so her half is in a "trust fund" held for her for when she gets cleaned up. if she dies after expenses it is given to charite. if she cleans up the money given is monitored in such a way that it isn't spent on drugs if she relapses. She of course is informed of all of this.  

[B1g_crunch]

I'd get the sister help to drop her addictions, then give her the money once that's done.

If it can't be done, and she keeps relapsing, I'd just give the money to charity.