What will Medicare cover for Mom's second rehab stay?

Just went to Medicare.gov. it looks to me as though this will all be part of the same benefit period, since there was not a 30 or 60 day time period when she was not getting rehab.

Ask the discharge planning department to check with medicare if her stay will be covered in full or if mom will be responsible for the $164 per day copay that is owed for days 21-100 of an eligible stay.

It depends on several factors, like whether this is the same problem or a new one.

Talk to the discharge planners at the hospital.

As long as it's seen as medically necessary, then they should.