My husband worked as a police officer with juveniles for 30 years and I have taught both middle and high school for the past 20 years. Unfortunatly this is too frequent. First, be sure the girl isn't a run-away or permanently living on her own (she may swear to you otherwise!). I would call CPS ( Child Protective Services) in your state and make sure you let the school authorities know. Even if there was someone assigned to take care of the girl they are negligent and the authorities need to know. I wouldn't tell the girl first because if she's a runner you'll lose her. God bless you for looking after this girl, I wish more responible poeple woud look after our youth. Usually it falls on our faculty to take care of our abandoned kids at affairs like this, it is nice to know others care. Let us know the outcome.