Hey there,
I'm really sorry that you had to watch your friend go through all that. The most immediate thing you can do is be there for her and help support her through this. She can get help, but it is really up to her - if she doesn't want to seek outside help, you can't force her to do so immediately. I'd recommend her calling hotlines that can give her practical advice on her situation (because what the authorities can do depends on what country she lives in, and I'm not sure what the situation is in America). However, it sounds like this has been going on for a while, and the fact that it has been suggests that she may not want to get the police involved.
I hope this helped somewhat and feel free to
PM me if you ever need anything!
Kyra