If you're only visiting 4 times a year she is likely more compromised than you think. Stop correcting her, stop arguing with her. It will not help. If she cannot manage her finances by herself even with remote help, you need to take them over. It would still enable her to live by herself with relief from the anxiety of paying bills and worrying about them.

With dementia, people who don't live with the person often don't realize how far down their skills have gotten.

Check her refrigerator and pantry for expired food the next time you are there. Check for multiples of the same item. If you find either, she may be unable to manage that either. Is she still cooking for herself?