My mother (87) accused me of "taking everything over"?

Mom has macular degeneration and now suffers from vascular dementia. I have been doing her bills along side her as well as balancing her checkbook, doing her laundry, for the past 18 months. I have taken her shopping, to appointments, to church, anywhere she wants to go for more than 10 years since she gave up driving. Recently, she has become very paranoid and has now accused me of taking everything over and plotting against her. She says she is not my mother and I am no daughter of hers. She used to tell people I was her eyes ears and she didn't know what she'd do without me. Now she is telling my siblings to not listen to my propaganda. My heart is broken beyond repair, and when I told mom my heart was broken, she said I have no heart. I love her and forgive her but don't know how to deal with this pain. I am going to review her bank statement with her tomorrow in the prescience of my sister and then suggest that they go to the bank and remove my name and add my sisters name to her account. That way I'll have no access to her account and someone lose can have that privilege. Right now it's the only thing I can think of to do. The pain is so raw I think it might overtake me. I do t know hat advice anyone may have but any insight would be appreciated. My siblings simp,y tell me to calm down and it's the disease not my mother. My question is how can it be the disease if in the same moment I am evil but another sibling is wonderful?