although maybe....but a very insightful book that includes info on disengaging with such a person is The Gift of Fear.  It speaks volumes on such compelling topics and is a must read for young women and all adult women.

But typically the abuser starts by breaking the spirit of their victim. After a while, they start to believe that they deserve whats happening to them. The only thing I can recommend is for you to be a stable presence. A friend who is consistent, and reliable. Don't bad-mouth her husband until she's strong enough to hear it, because she can always go back and say, "my friend thinks you're ....." which would only cause problems because now you'd be considered "the enemy".

When she feels a bit stronger, you can help her plan her exit. I had a friend who was in an abusive relationship (years ago). She kept an extra change of clothes, an I.D., some money and a credit card at my house. You can do that as well.  

As painful as it is to witness, all you can really do is be there for her. Good luck.

Haven't BTDT, but I agree with what Gloria wrote and I am a firm believer that you can't intervene in cases like this.  

People have to figure it out for themselves unfortunately.

All you can do is be there for them, call them a lot, try to see them as much as you can, and be there when the sh*t hits the fan eventually.

been in an abusive relationship myself, but I've "lost" a very dear friend to one (not to death but because she dumped me) and I must recommend that even when she's complaining about him, just listen and try to keep any strong feelings that come up in you in check.  There's nothing you can do, but if you're able to be present and stick it out with her, if she ever decides to leave him you can be there to support.

Lots of good advice above. I would add that it might be helpful to you to think about how emotionally involved you want to get with your friend's marital problems. If she is an old or very close friend, of course you are already emotionally involved with her as an individual, but I have found that people in troubled marriages sometimes are very self-involved, and lean on certain friends for some pretty intense support, while offering not much in return.

Sounds really harsh, I know. But I have been that steady presence for three friends over the years, and even if you don't bad mouth the husband, which I didn't, once you know too much, the person is liable to dump you anyway. Or the husband gets uncomfortable with the friendship, even if you generally have some empathy for the guy, with the same result.

One of my oldest friends (her son was my godson) did not show up to my wedding reception because at the last minute her husband did not want to go, and they had a huge fight about it. This is her second problematic marriage, and at that moment, I was totally over her and her relationship problems. I spent half of my reception worried in the back of my mind that she or her kids had had a massively huge emergency, or were possibly killed in an accident. Have refused to talk to her since, a sad ending for a 21 year friendship.

I can count on four fingers the friends I would support considerably with no reservation if they had serious marital problems, and that is it.

Sorry to be a huge downer, but that's my experience.