While I"m glad you aren't the culprit you fundamentally misunderstand one major concept:
It simply doesn't matter if she agreed to screw the entire La Lakers team at Mid-court during half time. She is a child and anyone who has sex with her is dead in the water. There is no "Moral" out here. When you are having sex with someone who COULD BE a minor BEWARE.
Again, the meth thing is the same. If she COULD BE a minor, you are responsible for her age if she is.
I know this isn't you, but you were obviously there as you said you "SAW" this go down. I'm sorry for the facts but they are what they are. She is a minor and not responsible for her stupidity in consenting to sex with a bunch of drugged out guys who couldn't have cared less if she was a minor or if she had aids. That's one of the main problems with drugs: Mental impairment.
So, while I understand and even applaud your concern for the friends of your that are about to go to prison for this, there just isn't much to do. The rest of the people present could easily be charged with contributing to the delinquency or aiding and abetting statutory rape or something having to do with the drugs. This is just the chance you take by living that sort of lifestyle.
As to my daughters personally? You are right, I would be on them so tightly that they wouldn't be doing meth, screwing druggies or for that matter, out of my sight for long enough to consider it. The real culprits here are the parents who failed to raise their daughter.