Does anyone know this movie?

I have no clue of what year it came out in but I think it was about a girl named Judy or Julie or something. Anyways she was at this camp and she was killing people and at the end of the movie she exposed herself as a guy. I forgot any other details. I was really young when my mom watched it and she wouldn't let me see it but I would sneak while she was watching it. Now I want to see it.