FMCA health insurance vs AARP?

My mother in law had a Humana Advantage plan which while cheaper than many others was terrible. Among the many shortcomings, when she had to go from the hospital to nursing home rehab they only paid for one week and then we had to fight for coverage every week after that for three weeks and then they denied all coverage.
Their customer service was terrible and for months after her death they called us wanting her to buy a policy even though they were told she was deceased time after time and they kept saying her death was entered unto their system.