There are some articles, in PsychCentral's archives, on this very subject. Unfortunately I can't provide you with links to them. (See my thread re: Question regarding the PsychCentral search bar on Bing.)

I suppose one question here is... is it your friend who doesn't want help or is it her husband & daughter who don't want her to have it? Perhaps though, in the end, it doesn't matter. The bottom line is, either way, you're not able to help your friend & your friend isn't receiving the help it sounds like she needs.

Depending on where you live, there might be govermental or human services organizations you could contact that might be able to help. That may or may not be the case where you live though. If not, I'm afraid there may not be a lot you can do beyond continuing to be there for your friend & to be as supportive as you feel you can be under the circumstances. Thank you for caring though.

P.S. Thankfully the search bar is now back. So here are links to the articles I mentioned above:

Denial is a Powerful Impediment to Treatment

How to Persuade Your Loved One to Seek Professional Help

11 Ways to Help a Loved One in Denial

12 Ways to Help Someone Dealing with Domestic Violence | The Exhausted Woman

Victims of Emotional Abuse | The Recovery Expert