My mother has always been in charge and decides what dosages to give. What can we do?

She can make decisions, even bad ones, as long as she is legally competent. Given her age, you are probably seniors too. You need to start small, maybe a house keeper for her once a week to do heavy cleaning (figure out which chores she hates and start with those) Maybe a bath aide once a week. Slowly increase the help as she becomes accepting of it. A gardener or lawn guy once a week. A window washer twice a year. Small steps.