How to overcome verbal aggression and mistreatment

I have a friend that treats her old mother very rudely, almost verbal aggresively most of the time. When we are together, sometimes her mother trust her feelings of sadness and despair that this situation causes on her to me and asks for advice. I’ve tried to explain the model to her (in a practícal way), but I really wonder if it is really healthy and fair for her to allow her daughter to mistreat her, even if she could manage her mind… I think she should manage her mind but also change her attitude towards her daughter, maybe speak her about her feelings with clarity or put some distance between them in order to stop the mistreatment. This lady’s late husband treated her that way and I think my friend “learned” that behavior from him. What do you think she should do?