Al I can say here is from my experience. I had a 'golden' childhood, but years later on MN I would post regularly on the stately homes thread, so what did I know back then? I drank a bit and tried to smoke weed. Wasn't very good at smoking as it made me sick, so at college I bought speed and got quite into that. Bought it off a dealer, one of my classmates. Took it all through my A levels, got them all, went off to uni. Not proud of it, but not really bothered by it iyswim. Never had drugs since. I used to like a glass or two of wine, but gave all alcohol up about 18months ago.
This is a longish life-I'm 48, good career, 2 amazing primary age DC. Perspective allows me to look back and shrug. I was a 'good' girl all my young life, even when taking speed. I knew I wasn't really into it, but I thought I'd take it for a bit. I knew it wasn't the answer, what ever the bloody question was.
I suppose I'm saying that what saved me(narc mother aside) was my basic sense of security from the family I had, particularly a loving father and siblings, and my basic good common sense upbringing.
Be there for her, my mother never ever was, I had to struggle through lots of things on my own, and I don't mean the drugs. Be there for her, tell her you love her, tell her that until you are sick of hearing it. She might pretend that she's sick of it too, but deep down she won't be. All that and boundaries for her, big boundaries about what you find acceptable and what you do not, and you'll be ok.
disclaimer...I may be projecting a teeny bit