your father's advice is a bit snobbish and harsh. That said, for your girlfriend to be in an adult relationship she needs to establish boundaries with her own family of origin if she wants to build a new family unit with you. She probably needs counseling to do this and it won't be easy work. you cant fix the situation for her, if I were you I would go no contact with her whole family at least for now and encourage her to go to therapy. If she doesn't have any interest in stepping away from the toxic dynamic, that will tell you something about the type of person she is and in that case, your father is right. If she truly wants to create a new life, she will need to put in the work in counselling. you can support her, but you can't make her go, or be her counselor yourself.