She signed a piece of paper revoking my POA and had it notarized, I don't think it is a legal document because it is not witnessed. My brother and family had her to change her bank account to put my brother on it and remove me. She has good days and bad days. She knows that she made a mistake but trying to get her to change everything back on a good day is hard. I don't have the money to fight for her to protect her and if I try to go to court they will contest.
As for guardianship, she would have to be ruled incompetent by the courts. This all takes money and your brother would have to fork over money to fight you. Then in the end a judge may see the sibling fighting and rule for an outsider to control her money.
Good luck to you. Maybe a honest talk with your brother would help.