I would be worried about the situation to. I have a 13 1/2 year old boy.
Needless to say there is no way in 1 1/2 years I'ld let him be in this situation.
The children these days don't have the same sense of responsibility and consequences of their actions.
After reading all your posts you clearly have a reason to believe she might not make the best decisions, if it were me I'ld go with my gut feelings and do what I thought would keep her safe.
People used to tell me I need to relax more because I refuse to get a babysitter that was younger than 17. They even used to laugh at me because my babysitter was a carer at my child are centre who I would pay $15 an hour to babysit for me. I didn't care because I know I was comfortable with my decision and knew that if something went wrong they would be capable of handling the situation.