[hocus pocus]

I agree with what Kyra has said. I think you should encourage your friend to get help, but I don't think you should tell anyone in authority about her situation unless you think her life is in danger from her parents or herself. Abuse of all kind is difficult to deal with, and it is important to allow someone to get help for themselves when they're ready if that is possible.

In the meantime, you can show her some resources. You can show her some hotlines that she can call to talk to someone about how she's feeling. You can even show her TeenHelp if you want. You can recommend that she finds ways to express her feelings, like through writing or drawing.

Another thing you can do is be there for her. Your presence, even if you're not talking about the abuse, can do a lot of good. You can help distract her, or just even sit there with her. When in doubt, ask her if there's anything you can do that she would find helpful.