How can I tell my friend without her getting angry?

[Ilike Cookies]

Ask her why shes telling everyone else about what her and her boyfriend do. Maybe(!!!!) just make a little fib and say some people are talking about her saying shes a slut and that its because shes telling everyone it. and at the end say "Well i was just letting you know because i didnt think it was right of them to say it." If she asks who either say you forgot and heard it when you were walking past a room at school and heard someone talking about it. Or just say someone at school.
Good luck!