Bung, I'll take your word on why your Mother does what she does, which is convenient since I don't know her.
You'll get lots of advice from others that wish to help but also don't know her or you and the family dynamics that have been in place for years. Pick your battles, ask yourself is the battle worth it? If it is then fight it, if it is not then blow it off and don't sweat the little stuff. The only committal advice you'll get from me is: Make a decision one way or the other, accept the consequences, NOT making a decision will tear you up worse then making a decision.