Encourage her to get started with counseling!!!!!
She definately needs to get out of the abusive relationship and the relationship with her new man. I suspect this new guy is a substitute for a father who takes care of you as well as a source for romance. Since he's unmarried at 47 and having a woman living with him whom he kicks out, I already know he doesn't know how to nurture a relationship.
Even if he could take care of her, I have never seen a rebound relationship last. Already she knows how this new man treats a woman when he decides to take another one. She is causing herself more pain and grief now and in the future. She needs to know why she makes decisions that cause her more pain. Isn't it painful to see her husband cry and plead? Won't she cry when the new man finds someone else?
Help her find support without the entanglements of a romantic relationship. That's what women friends are all about.
I also feel so very sorry for that baby. The baby's needs should come first for the mother. It sounds like she has so many needs herself that she can't focus on the baby. Perhaps she should allow the baby to be cared for by someone more able to provide for his emotional needs. The obvious one unmet now is a sense of security. These little babies are born with a great sensitivity to their surroundings and relationships. That is how they are able to survive. The first 5 years are crucial in a person's life. If their many needs are not met, they have the sort of problems this mother is having now.
When my mother was too depressed with postpartum depression and my father couldn't care for us full time (he worked 2 jobs) we kids lived with an aunt and uncle until they got their life back together. That isn't the ideal but it's sure better than living with parents who are overwhelmed with their own needs, fighting and crying and looking for security for themselves "in all the wrong places."
To be successful in a new relationship one must be finished with the old. That includes both a physical and an emotional divorce. Everyone needs to learn about themselves and about their decisions and actions that created the old relationship. We must learn how to develop a new relationship without repeating the old.
I wish her the best. If you don't spend time with her you cannot do anything, even offer advice. Perhaps you can share these answers with her friend so that she has insight into what is happening and hopefully make suggestions to her friend that will cause her to think again about what is happening.