i sooo agree with pinipig the ER doc. I am an OB doc who had foot surgery a few months back. i was not allowed to walk on the foot for 6 weeks. I rented a knee scooter (he called it ankle scooter- i looked at the pic- same thing I used) i rented from "rentakneewalker.com". but i would shop around for the best price, they change from time to time. and cheaper than renting a wheelchair at disney- i paid $30 a week.
they deliver it right to your house and you ship in back in their box- they paid the shipping. if you don't want to bring it on the plane you could have it delivered to disney, but it certainly would be allowed and easy to get onto the plane.
i was able to return to work in 2 weeks, fully functional- even did deliveries and surgery on it!
they are very comfortable, very portable, and really FAST! i raced lots of nieces and nephews on their bikes- you can't keep an old person down!!! you just scoot with one knee on the very comfortably padded knee rest. just like a regular kids scooter- it will be an easier trip for her than if she were walking! one hint, the plastic knee rest gets wet if you are out in hot temps, in buildings i was fine. when traveling long distances outdoors, and i did travel ALOT, i just brought a washrag and put it on the kneerest.
you will need to bring her crutches to get up the bus steps, but you could leave them somehwhere near the front of the park rather than carry them. don't think anyone's stealing crutches at disney! let me take that back- i took a bus trip during the time i used them and didn't have crutches- just didn't bother to get them because i didn't need them (i thought! didn't plan on a bus trip!) anyway, i literally crawled up the steps of the bus on my knee and stepped right into the front seat of the bus when i got to the top. so if you really don't want to bring crutches, and you have no pride!!!!! or dignity!!!!!- then crawl up like i did. worked just fine
i would never let this interfere with my full enjoyment of a long planned and dreamed about disney trip. just don't give up or give in. she can do this!