DD is handicapped (Cerebral Palsy) & we use a wheelchair when we cruise because it is safer for her, & faster for us (she can walk, but has poor balance, so crowds are dangerous and is very slow). She is not very tall(5'1") so I can't speak to the height issue. For safety's sake, we ask for a shower chair for the shower stall, this might help your wife so that she doesn't have to balance. Also, while we didn't use this, there is also the option of a toilet seat riser, which is basically something that's about 6-8 inches high (I think, don't quote me on that) that sits on top of the seat & makes it easier for those who need extra leverage for sitting/standing from the toilet. Just fill out the special needs form
https://secure.royalcaribbean.com/allaboutcruising/guestSpecialNeeds.do
You can specify what things you might need.
Also, you don't mention which ship you are on, but find out if there are any family restrooms, in case she will need assistance while you are not in your cabin -- even using the handicap stall can be a challenge, even when you are just the one assisting the person who needs it.
