Welcome to disABILITIES.
First, for getting the walker on the airplane; most walkers fold up. It may not fold to be shorter, but usually the sides fold in so it can be made more flat. That way, it should fit in the planes' closet (most, but not all, planes have closets). Depending on how small it folds, it may fit in the overhead bins. If neither of those work, you can gate check it. She would be able touse it to board the plane and leave it right outside of the door of the plane. It would be waiting for her in the jetway when you get off the plane. Ask the gate agent when you first get to the gate (before boarding).
For rides,
here's a link to a thread about boarding. She would be able to keep the walker with her until boarding and then (for most rides ), it would be waiting for her when she gets off.
i don't know if you hav ever been to WDW, but she probably does not realize how large it is and how much walking is involved. Just to go around WS in Epcot is over a mile. You can easily walk 6 or 7 miles a day. Someone who has been on a couch for several years is ging to be pretty miserable after a few hours.
This website has some good hints for talking someone into realizing they need a wheelchair or
ecv. If she absolutely refuses to get an ecv, the WDW resorts usually have some wheelchairs available to lend free of charge(first come, first serve, may be all loaned out or what they have may not be a size that you need). The price is rght, but using a wheelchair means someone needs to push it. You can also rent wheelchairs at the parks, or from one of the offsite rental places:
Care Medical:
http://www.caremedicalequipment.com/
Phone (407) 856-2273 Toll Free U.S and Canada (800) 741-2282
Walker Mobility:
1-888-726-6837
www.walkermobility.com
RANDY'S Mobility is in Kissimmee 407-892-4777
http://randysmobility.com/
Colonial Medical
http://www.colonialmed.com/about_cms.html
(800)747-0246
http://www.scootaround.com/ Not much feedback. Several people who reported they had no problems.