Your situation is far too complicated for this simple online Q&A forum. Speak to your attorney. If you don't have private counsel, hire one who can advise you about elder care, estate planning and possible guardianship.
Go to court and try an action for undue influence and appointment of a neutral qualified conservator.
My name is Stephen R. Cohen and have practiced since 1974. I practice in Los Angeles and Orange County, CA. These answers do not create an attorney client relationship. My answers may offend I believe in telling the truth, I use common sense as well as the law. Other state's laws may differ.. There are a lot of really good attorneys on this site, I will do limited appearances which are preparation of court documents it is , less expensive. However generally I believe an attorney is better than none.
If mother retains capacity, she could revoke her current financial POA, and sign a new POA appointing a trusted agent. Also, mother could set up an irrevocable trust outlining her estate plan, to protect her and her plan against the financial abuse. All of this would need to be discussed with and set up by an attorney.
--Ashley Payne, Elder Law Attorney in Richmond, Virginia
This answer is meant to be general in nature and should not be construed as legal advice. Also, this answer does not create an attorney-client relationship.