I think she should stand her ground and make the decision that she feels are best. The problem in telling them the reasons for staying or leaving is that children have a strong allegiance to their father. They often don't see or believe that their father is this negative person. It is best to just maintain one decision and live for that decision. If a child has a strong allegiance to mom then she may find a confidante but that is a very slippery slope. If she chooses to stay just for the children then she has to bear the repercussions of that decision. If she feels this is for the children then telling them may make her appear self serving. Instead she has to decide what she wants for whatever reason and live with that decision. Unfortunately it would better for her if she realized that in the end the children don't want her to be miserable.
Please provide positive support or I am not compensated