Kicker is right. Some people just live to be the drama in everyone else's life.
I don't know what happened in your sis's life to make her lash out at the world, but there is nothing you can do to make her want to live up to YOUR expectations.
Have you ever seen the show, *Intervention*? You might want to watch that. If you don't have the channel on cable, have a frined tape it or look it up on the net.
I think you'll see that there are ways for you to stop feeling bad about how she lives, stop feeling like there is something you can do to change her, and stop letting her suck you in every time her world implodes.
You don't need her stress, you have enough of your own.
Trust me, I've had a couple of these drama queens, men and women, around me. all they do is suck the life out of you. The best thing for evryone is to get some distance, let them either work it out or crash and burn - they're going to do it anyway, they don't need to drag you along for the ride.
As for me, I'm sick of the hospital visits, the courts, the jails, the drunken/drugged up calls at 3 am.