Another thought - might she be better with an animal friend? Could you convince her to volunteer at a shelter, even in a desk-type position that she could manage with her walker?

Animals can listen to vitriol all day and still will love you, if you love them and are responsible enough to care for them. Maybe an older cat or dog that doesn't require much exercise would help her focus on the present, and now dwell with such bitterness on the past? There's nothing like a cold wet nose or a persistent tapping paw to get one out of bed in the morning ...