Hi, I'd like to help you with your question.
There are many resources out there for women who have been in domestic abuse situations. Here are some resources to help you:
Family and Friends' Guide to Domestic Violence: How to Listen, Talk and Take Action When Someone You Care About is Being Abused by Elaine Weiss
Domestic Abuse: How to Help (Resources for Changing Lives) by David Powlison, Paul David Tripp and Edward T. Welch
Finding Your Way Through Domestic Abuse: A Guide to Physical, Emotional, And Spiritual Healing by Connie Fourre
It's My Life Now: Starting Over After an Abusive Relationship or Domestic Violence, 2nd Edition by Meg Kennedy Dugan and Roger R. Hock
Mommy's Black Eye: Children Dealing With Domestic Violence by William George Bentrim and Ms. Christi Schofield
When Dad Hurts Mom: Helping Your Children Heal the Wounds of Witnessing Abuse by Lundy Bancroft
Here is a link to an excellent resource on line:
There are many support groups and other sources of help on line and in the community for when your girlfriend feels ready to deal with how she feels. It may be that she was so traumatized that she is unable to face what happened. These resources should help give you ideas on how to approach her and help her through this pain. I also included a few books for your girlfriend's daughter. She may be at a different place with what she experienced so hopefully the books will help.
Let me know if you have any more questions I can help with,