Having so many sexual partners by age 15 is concerning, especially while she is so unsure of herself and her body. She could easily get pregnant or get a STD. I would focus right away on talking about safe sex and get her on birth control if she wants to continue having sex with boys. It could be she is -trying out- being a female by buying lingerie and dating boys to see if it is tolerable, but what she wants most of all is to be a boy. She may have been thinking of this for a long time. You dont seem receptive to her changing genders right now, so she may be making the most out of being female. If she still wants to be a boy, I would say you will honor this and use whatever pronoun she wants as long as she starts seeing a therapist right now. She definitely needs guidance. It is possible that she doesnt identify fully with either gender, but destructive behavior is my biggest concern. She may be putting the cart before the horse by deciding what gender she should date when she is most unsure of what gender she herself should be. I would tell her she should focus on herself and worry about who she is attracted to later. Not everyone will fit into a stereotypical box. Best of luck.