What insurance plans are best for Mom's pre-existing condition for cancer?

My mother (age 73 )is being treated aggressively for colon --> liver cancer this year in Florida.Before this she has not been sick. She has Humana insurance(medicare hmo ) and has receieved some grants for the copays. It is getting towards the end of the year and she is looking at changing insurance policies to one that would be most suited to treating her illness. My parents are also planning a move back to Ohio sometime this coming winter. We are confused about which plans would accept her pre existing condition and also how making a move out of state would affect the choice.