Mom having difficulty with Grandma. Any advice?

So first of all, it's really my husband's mom/grandma. They live in Merida, Mexico and we only get to see them a few times a year. My husband is the only person grandma trusts and who can calm her down when she goes into her tail spins. Unfortunately, we can't move her to the states because we don't have our own place (another long story). She frets about money constantly and wants to always look at her balance online and every time she comes to the states, she wants to empty her bank accounts and we always have to talk her out of it because it's too dangerous for her to travel with all that money and she forgets where she puts it. It's just a mess. Mom can't get her to go to the doctor to even get tested for her memory loss, but it's clear she has some type of dementia (she's 90). Lately she's been accusing Mom of poisoning her, which is not true at all, and claims everyone is stealing from her. Mom wants to change things around so that she can't make any financial decisions and she wants to get her to a doctor. How do we accomplish this?