Hi, Rafael! How thoughtful to want to celebrate your wife's birthday with this fabulous surprise! I hope you can make it work!
If your mother-in-law is on peritoneal dialysis, where she does the exchanges herself, she can contact the company that delivers her supplies to her home and arrange for them to be delivered to the resort. My dad, who did this type of dialysis, would just call a couple of weeks prior to his vacation, and his medical supply company would deliver the amount of supplies he needed for the duration of his vacation, and they would be delivered to the resort. You can also phone ahead and let the resort know to expect them. it helps to put the room in her name so the supplies are properly routed.
If she is on hemodialysis, where she has to go to a dialysis center to do her exchanges, she must make arrangements in advance. It helps to have her dialysis center help with this, as they will need to provide some medical records. It is crucial that you plan ahead, so she can dialyze in Orlando on the same schedule she does at home. There is a national chain of dialysis centers called DaVita, and they have eight Orlando area locations. Her dialysis center is probably familiar with them, but I know they are relatively easy to get to from Disney World, and with eight centers, you might find scheduling easier with them as well.
With regard to walking, there are wheelchairs and electronic convenience vehicles (scooters) available at all of the theme parks for you to rent. You can find all the information on rentals
HERE .
I hope your wife's birthday vacation is absolutely magical!