I've been where you are....my son decided to go to this camp and there he met a family who were neglected. There were 5 kids and the father had died young..........Mom was trying to make ends meet, but not doing a good job at all with money or the kids.........the one son, got a job, she took all his money except for gas, I don't think he would have eaten much without us.......another son, well, he was just a thief.........my son was insistent on helping these kids.......they were around 10 at the time....the thief was younger........
To make a long story short, I talked to them all, tried to help, tried to defend them and make them see their Moms points, even when she was wrong and I told them she was wrong.............One son is no longer really friends with my son..........he has changed a lot and rebelled much......he's 30.....the other son, (the thief) he and my son are still friends, and he demanded I come to his wedding!!! He said if it hadn't been for me jumping on him, telling him he was wrong, making him be at least thoughtful, he would never have been as happy as he is today............I was honestly shocked, surprised and happy all at once........my son was in his wedding.....and we had a great time...he has 2 kids now and he's doing ok.....
So, I can say all the things that everyone else has, and they are right, but I can also tell you, that if this child needs someone, someone to help them be a better person, then, you might be the one to help.........these boys became part of the family, literally...........not my choice at the time, but my son was right...........
So, talk to your daughter, get her take on things, find out what she wants and what she thinks...........and don't look at yourself as a babysitter, but a mentor..........this child obviously needs one..........
Take care and I wish you luck in your decision here.........you have to do what you think is right for you and your family..............this girl in NOT your problem, but it is your decision.
Hang in there.