S.,
I am concerned about this. I would start her in counseling with a good child therapist right away. I am not saying that anything bad has happened to your daughter, but you need to know. Even if she just witnessed something or has heard him say things, it can leave lasting issues. I have a 24 year old son that suffers from Post Tramatic Stress Disorder and other anxieties, just from hearing his father verbally abusive me. As a teenager, he would sometimes snap and become physically abusive. For him it was complicated because he has learning disabilities and has very limited expressive language, so he went mis-diagnosed until just a few years ago. I quit a very good job and lost everything just so I could devote my time to him and get him straightened out before something really bad happened. Once I figured out what the issues were, the solution came quickly and I had a totally different, very happy son in months.
The sooner you find out what is troubling her and help her to deal with it, the better. Not just for her, but all three of you.
M.