I cannot believe after all of your upset, you did not go to this friend's house and drag her drunken azz out of there in the early morning...YOU allowed her to think there was no consequences for her actions again. "shecame home late this afternoon"...this *adult* has zero supervision. You did not talk to the other girls parents? you are allowing her behavior to continue by staying silent and not putting your foot down. You have to be pro-active and unpopular with your daughter...at this point there is really no room for your own fear.
I hope the next time you post you are not doing it from the ER or the local jail...and YOU as the parent will be held responsible by the police for knowingly allowing underage drinking....in my town there are billboards posted that state this fact...."parents will pay the price"....maybe the only way to get through to them is hitting them in the pocketbook?