Figaro is right.
Electric (power) wheelchairs are very differnt than
ecvs. What your mom wants is an
ecv, which you can rent from the parks or from one of the off-site rental places.
Manual (push) wheelchairs and ecvs can be rented from the parks, but they are first come, first serve and they can sometimes run out. They are unlikely to run out of wheelchairs unless you go during a really busy time, but people have posted getting to a park a few hours after opening and finding all the ecvs were already rented out. The wheelchairs and ecvs are not allowed to leave the park they were rented from. There is no guarantee that one will be available at a second park if you park hop.
The resorts have a limited number of manual wheelchairs to loan, but they don't have ecvs. Some people have reported good expereinces with getting a wheelchair from their resort. Others have found the available wheelchair was not in good condition or not a size they needed. People have reported it took from minutes to days to get a more appropriate one. So, eve if you plan to get one from the resort, it's a good idea to take the rental info along.
Here's a list of off-site places that DIS posters report renting from:
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.
All of them have had good reports and will deliver to your resort. Randy's requires that you be there when they deliver (which might be an advantage fro someone who has questions or needs a demonstration). The others will deliver and pick up from bell services.
When we inquired into renting a power wheelchair for DD because we didn't want to bring hers from home on the airplane, we were told we would have to provide measurements (although they could not necessarily provide a wheelchair of the exact size) and all the settings to program the controller. It's not something you can rent unless you already have one.