First of all, tell her it will make the trip miserable for EVERYONE, including herself if she tries to walk. For example, World Showcase in Epcot is over one mile.
However, instead of a wheelchair suggest that she rent an
ECV from an off-site company. This will give her the "freedom" she feels she needs and will not have in a wheelchair.
As a matter of fact, with an ECV she can run errands for people and also act as a "sherpa" in carrying items.
Some information for off-site rentals are:
Walker Mobility:
888-726-6837
www.walkermobility.com
Care Medical:
http://www.caremedicalequipment.com/
407-856-2273, Toll Free U.S and Canada (800) 741-2282
Randy'S Mobility is in Kissimmee
http://randysmobility.com
407-892-4777
Colonial Medical
http://www.colonialmed.com/about_cms.html
800-747-0246
ScootAround
http://www.scootaround.com
Toll-free, US and Canada 888-441-7575
I have used Walker a few times. They will ask for a credit card and charge it the day before arrival. They will deliver the ECV to your hotel bell services before your arrival and pick it up there after your departure. Their rates, especially for longer than a week, are much better than Disney's. Also, their scooters are much better.
You might go to a Wal-Mart or large grocery store and have her practice with one of their
ECVs. Just realize the rentals are smaller, quicker, and easier to maneuver than the store ones.
Since you are using a car for getting around, the ECVs break down into five pieces, the heaviest about 39 pounds. They take about a minute or so to take apart and about two minutes (once you are used to it) to put it together. Just be sure you rent at least a full-size, four-door sedan with a large trunk (Buick Century or larger).
Definitely bring the HP placard. The medical/disable parking areas are strictly enforced, and it is a $250 ticket down here.
Normally the best accessibility, especially with an ECV or wheelchair, is to use the car for everything EXCEPT the Magic Kingdom, buses are best for that.
If you want more information, or how to disassemble or assemble an ECV just ask.