NP here, and I have to say I think you are handling this remarkably well by putting your daughter's feelings and well being ahead of your own. You are correct not to confront him. That simply never works.
Your statement that you think she's deeply ashamed and scared is what jumped out at me like lightening. I'm inclined to think that's where your focus should be. I work in the field, but I must confess it's been a while since I've done direct service with victims of domestic violence (I do policy work now) but I do remember an effective strategy is asking a lot of questions - what are you most afraid of? What's the most important thing to you right now? Do you see that happening the way things are? What do you want to see change? How might that happen? What does a happy life look like to you? Does this match that? You know him best, what would be the best way for you to leave without making this worse?
That kind of thing. They aren't all artfully stated or well-thought out but asking questions puts her in the driver seat of her own life. It gets her thinking with a sense of autonomy about her own life.
The hotline is a great resource, but should you need more intense legal advice, check out Break the Cycle. They specialize in teen and young adult domestic violence and have attorneys on staff to assist. I'm not sure where you're located but they have an office in DC.
http://www.breakthecycle.org
Good luck and keep posting if you need to. I think there are a lot of us out there who have experience in this and are happy to weigh in as you make your way through this.