My sister had our mother live with her for 3 years until our mother's angry and seemingly manipulative ways became too much for her and her family. She is now in the nicest retirement facility she can afford. I have had power of attorney to pay her bills, taxes, etc, but now she thinks she can and should handle her finances and plans to revoke it. (She has not officially been diagnosed with dementia, but the track record of failing memory is quite clear.) I fear that if she does revoke POA, she'll not have enough money left when she absolutely needs a memory care facility. But I feel powerless - there is no reasoning with her and she won't acknowledge her limitations. What can I do?