I don't think you have dealt with dementia yet. In that case, speaking "against" what insulting things your parent says is necessary to protect them from harm. You say to her caretakers - "she would have never said that awful thing if had she her senses. Forgive her, please." And you tell you mom to shut up and stop misbehaving. Roles shift.
Do they ever..My sojourn as her parent is over and mother is with her Father in heaven..The change of roles for me is over..until I become the child, a reality I may face. May God comfort and strengthen my children if this occurs.