My Sister

She has moderate dementia and getting worse really fast. I have tried to help her with decision making and financial decisions, but she gets very angry with me like I have never seen before. At this point I don't think she trusts me. She will make a good decision one day then the next day she has changed her mind. Her only child and his girlfriend moved in a few months ago. They have tried to turn her against me and my other sister. They are verbally mis treating her and she has called the cops several times to get them out of her house, then she lets them back in. They are also taking advantage of her bank accounts. My hands are tied. I am so frustated.