I am not discounting your suggestion at all, Browncoat. She could totally try it. But it's not likely to change anything and that is the truth.
People who do this habitually ... nothing will make it change unless THEY want to change, whether she leaves for a day/week/ or not.
It's a living hell. It's truly the only way to describe it. I just feel for her because she has kids and they are growing up prob thinking that is a normal family dynamic or may even repeat it themselves down the line or think they aren't good enough for their dad to speak to them. Sad.