I have known a LOT of people who struggle with hygiene as a result of abuse. Dry shampoo is a wonderful item.
I would just say that if a persons teeth have gotten to the point where they hurt, it may be worth looking into dentures. Dental pain starts slow, but will drastically impact your life. I know they’re expensive, but it might be worth letting go of something stressful and painful.
And please remember that daily bathing is a recent occurrence. In 1950s America everyone bathed once a week and thought nothing of it. Before that, they bathed even less frequency.