It seems to me that you are doing the best you can with the situation you have. After reading all the responses it is obvious that you have hit a nerve with many women. One thing I would say is that trying to have a conversation or set boundaries with this type of person is not going to be helpful. I think of it as hitting your head against a stone wall. All you get is a sore head!
You will need to disengage and only make statements to this person. I know that you want to have a healthy relationship as she is your mother, but you need two people involved to have a relationship and you can’t do it by yourself. Best of luck.