S.M.
My father was physically abusive to my mother. It ruined the first 21 years of my life and had the potential to really interfere with my adult life.
She absolutely needs to leave him. And she must make sure she is on birth control, even if she has to keep the pills a secret from him. The best thing she can do is come up with a secret plan to escape from him. Contact your local abused woman's shelter.group (look up National Coalition on Domestic Violence for referrals). They can advise you how to safely help her and maybe it will be the boost she needs to contact them. Tell her it never hurts jus tto talk to someone. Men like this pick isolated women or isolate them themselves. She need to get into a support group and work with a DV counselor.
These gusy are able to continue to do this because they use fear. Unfortunately,many of them are very very dangerous. So I understand your discomfort. I would not suggest you offer her a place to go, since he may come find you - and I suspect you have kids. But I do think you can help by storing belongings for her, going with her to set up a secret checking accunt in her name, and whatever else she may need to do to get away. If you can gift her or front her money to put down a security deposit on an apartment, that would probably be a big help because he probably monitors her money. And in general, just support her and encourage her to do the right thing,
In the end, she has to make the decision, and you have to stay safe. I really admire you for wanting to get involved in some way, because most people don't. I had relatives walk away saying it wasn't there business. You can't imagine how de-valuing this can feel. Even though you are realtive strangers, she nees to know she has an ear and some sort of support. And a kick in the behind ot act on the informaiton is good too.