Hi, missydisney!
To have your room request changed to guaranteed medical necessity, you will need to talk to the people at special services. Their number is: (407-939-7807). They are the ones who can make sure that you are guaranteed a roll-in shower handicapped room. I know that as Disney refurbishes the rooms, there are now handicapped accessible rooms with double beds.
Also, if you have any other questions come on over to the disABILITIES board, as the people there know absolutely EVERYTHING there is to know about that kind of stuff(smile).