One of the things I strongly resent from my time spent in the program is that I never had the opportunity to experiment with alcohol when I was a teenager. I had never been drunk before the program and for several years afterwards I was too terrified of ending up "deadinsaneorinjail" that I wouldn't touch alcohol. As a result, I didn't know my limits or even how alcohol really affects you. So, I was totally unequipped to deal with it in a social setting. When I finally did start experimenting with alcohol (very lightly and only a few times), I was already working on a career and in a very important relationship. I had several painful episodes before I learned how to drink responsibly - nothing horrible, just my partner probably didn't need to see me make out with our roommate's girlfriend one New Years

, and my boss had a really good laugh at my expense at an open bar office party. It would have been so much easier to have had that as a teenager when the consequences aren't so immense.
Also, in my opinion, most parents don't give their kids as much credit as they deserve with respect to their friends - especially in the case of girls. Chances are that at least some of the people your daughter hangs out and drinks with are genuinely caring people who have no malicious intent towards her. Her instincts will keep her away from those who may be predatory and dangerous. When her thinking is impaired by alcohol or drugs, those she's chosen to spend time with will likely keep an eye out for her. That's the way friends work - even silly teenage girls.
What I would do (and what I did with my younger sister while she was in my care) is to provide a safe place to come back to. That is, calmly educate her about the real dangers of alcohol poisoning and signs to watch out for in herself and the people she parties with. Talk to her about date rape and how to keep herself safe (always stay with friends she trusts, guard her drinks, etc.). And above all, always make it possible for her to feel safe asking you for help. Let her know that she can always call you if she needs a ride home or feels unsafe. If she does ask for help or confide in you in any way, never, ever punish her for it. Make sure that she understands that you are there for her when she needs help, no matter how much she has disappointed you.
A lot of that is extremely difficult to do. It may get worse before it gets better. She is going to make mistakes, make very stupid decisions and scare the shit out of you. That is how we all learn. As parent it's our job to be mature, responsive and loving - even (especially) when they are not. In the end, all of your patience will reward you with a lively, independent daughter who respects and trusts you.
Best of luck!
Rachael
BTW, here's a student produced PSA that actually has some very valid advice regarding date rape (ignore the lame dancing

):
http://www.youtube.com/watch?v=hvOpN-QQs_U.