Reporting my daughter's friends assult

My daughter's fifteen year old friend confided in me that while she was on a school camping trip her classmate started to touch her on her breasts, she said she was first into it but then said stop which he became more aggressive. He put his hands on her vagina and backed off when he realized she had her period. She has been numb and anxious ever since. I told her she really needs to tell her mom or guidance counselor but she hasn't.

As a mother I would want the other mother to tell me because it's a traumatic event and could impact her for the rest of her life.

I also don't want the teenage boy to think he can treat women this way. I told her she needs to set a time limit and talk with someone or I will have to report it. Now she is upset with me and I feel awful. I don't know what the right thing to do is. Help!