She'd still have Medicare, part A & B, she just wouldn't be enrolled in the HMO. (I'm making an assumption here about her plan.) So she'd have to go out of pocket 20%. Does her current plan include prescriptions? That might complicate things further if she doesn't have a separate plan.

If she has very little income, then she very likely qualifies for Medicaid. In CA she would. Many people that qualify don't bother applying. That's where I would start.

And, they probably sent her a huge booklet a few months back letting her know which docs would be eligible and which wouldn't. The kind of thing most of us ignore, so I doubt her rights have been violated. She needs to figure out how important it is to her to stick with her current treating docs. Will this docs accept Medicaid if she qualifies, etc.