I agree with Zoso, it often takes several tries to stop drinking or using. That said, some people just stop and are done with it. The thing is, nothing you do or don't do will affect the outcome, she's on her own to find a better path.
I too have a member of my family who estranged himself a long time ago, a brother who was never close to anyone except his own wife and grown children. No reason, nothing specific happened, he just doesn't talk to anyone except at funerals where we all pretend he just has been busy on the far side of the planet...when in fact he lives only a couple of hours away.
For several years I would send cards on his birthday or at Christmas and enclose a personal note updating him on my family and still he ignored. I made my peace with this and accept it for what it is today. We can't "make" someone be family.
I hope your situation gives you a chance for some dialogue with your sister, regardless of the outcome. This alone may bring peace to your heart.
Hugs