AO, I work professionally in the field of domestic violence. Your friend is, indeed, fortunate to have survived, but this experience has traumatized both her and her child. I don't know where you live, but most prosecutors' offices and communities have lots of resources available for victims of domestic violence--there are counselors and advocates who can help with safety planning, processing the trauma, etc. She can either contact the prosecutor's office and ask to speak with someone in the DV or victim-witness unit, or call the local women's shelter or the national domestic violence hotline, and they will hook her up with whatever she and her child may need.
What YOU can do, as a friend, is to be supportive and help her to realize what an extremely dangerous situation she is in. She is likely to be subjected to manipulation and intimidation by the abuser, his family/friends, and maybe even her own family (depending on their view of the situation). There's a good chance that at some point she will want to take him back, to forgive him, and to minimize what happened. There are good reasons why victims do that. Try to be as understanding as you can, but encourage her to allow him to be held accountable for his actions. Abuse gets word, not better, over time. There might not be another chance for her.
Hugs, thanks for being a good friend.