Should we have a Medicaid case worker help us with choosing an HMO?

No you don't need and can't get a supplemental prescription plan on Medicaid. It's already covered.

I'm not aware having an HMO if you have Medicare and Medicaid. BarbBrooklyn is right, though. I'd discuss it with her Medicaid worker to see if you need a Medication supplemental policy. My cousin has one of those that covers Meds cost that Medicare and Medicaid doesn't cover. She can explain if that is needed in your state and how it works and if she can get extra help with that cost.

I believe that your mother should have been assigned a Medicaid worker when she became eligible. You might need to call the number on her card to find out who the worker is.

As to accommodations, I'm assuming that your mom was assessed when she was accepted into the AL she resides at, and that they felt they could meet her needs. Are you seeing problems arising there? If you can be more specific about what issues are arising, you will get better advice.