Welcome, Sisterstruggle. So sorry for your pain. I would suggest that you do a search on this forum with the word "sibling." You may find some other soul sisters and brothers here. And lots of mommas who can help, too. One thing to know, hard as it is, is that you can really do very little to change the outcome. She's in charge of this one.
Yesterday my 14 yo daughter was able to convince her BF that he needed to go home, talk to his mom, and fess up to his pot, alcohol and other drug use. Her joy in being able to convince him was like a drug in some ways. She watched her sister in the hospital for 5 weeks after a heroin overdose and she has found too many friends of her own to be vigilant with since. I am seeing both sides right now. Or three sides! My own addiction to helping my AD, my AD's recovery process which involves being nasty and/or cold with me, and my youngest daughter trying to rescue everything she can find! (Look at my post about the baby hawk incident!) You need to find a way to detach from her decisions, good or bad. I know you can do it. You seem like a smart sister. Peace.