Observanteen
I think the best move would be to find either a head staff member or one of the morahs or mechanecheses or whatever they are called in these camps and explain the situation. I would recommend speaking to one who you think is openminded and understanding and will not try to get the kid kicked out of camp and will also be able to talk to the kid and maybe explain what’s wrong about what she is doing. The person you speak to must have a good understanding of Chinuch and be able to understand the kid and where she is coming from…
That’s what I recommend. If you don’t think there is anyone in camp who can help her then contact someone from out of camp like Rabbi Wallerstein…
Hatzlacha Rabbah with this situation. I respect that you care enough to want to do something about this and I hope you will be Matzliach in saving this girl from messing up her life.