I definitely say a monorail resort. I know with lots of medical equipment, likely on her wheelchair, avoiding ANY buses may be nice! I get nervous when bus drivers tie me down WITHOUT having medical equipment on the chair. I much prefer taking the monorail where you will just be able to wheel her on and then take a seat. No fussing with straps.
Of the monorail resorts, if a Bay Lake Tower villa is not an option, then I definitely go for the Poly. It has a zero entry pool, so no need to try to lift her in and out.
How likely is she going to want to do Animal Kingdom? Pretty much no matter where you stay, I have found getting to AK is a bit of a hike, you must take a bus no matter what. If she has temperature control issues (which I do) then mornings in AK are best. It is much cooler and all the animals are out. I don't know what her sensory and vision capabilities/desires are, but AK has two WONDERFUL shows that are indoors.
If you are going to spend most of your time in MK and Epcot (which I think has most of the best stuff for someone who cannot transfer/cannot transfer easily), then a monorail resort is best.