It looks like one of the DVC moderators moved your thread to the disABILITIES Board for you.
Besides the good info you already have received, I have some links for you.
First, here's a
link to the DIS page about touring with mobility disabilities. It has a list of rides/attractions where your mom would be able to stay in the wheelchair or
ecv for the whole ride/attraction. As was already mentioned, the park maps also indicate this information. If there is a little wheelchair icon, you can stay right in the wheelchair/ecv. For rides where ecv users have to switch to a wheelchair, there is a little icon that shows an ecv with an arrow to a wheelchair. For those rides where everyone has to get out and transfer to a ride car, there's an icon of a person in a wheelchair getting up.
AK and the Studio are almost totally accessible (because they were built fairly recently). MK and Epcot have been retrofitted to make them pretty accessible, although (especially MK) not built totally accessible to begin with.
For each park, there is a Guidebook for Guests with Disabilities that you can pick up at Guest Services at the parks (they sometimes are availble at GS at OKW too). They are helpful about general boarding info; they are not very specific, but do have information about which rides, for example, have moving walkways. There is a currently active thread on the disABILITIES Board about ride boarding.
If you decide to rent from one of the off-site wheelchair/ecv suppliers, here's a list of the ones DIS posters have used and posted about many times:
Care Medical:
http://www.caremedicalequipment.com/
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
OKW is a great resort for someone using a wheelchair or ecv. Because the rooms are large, it's easy to use a wheelchair in them without trouble. Also, having the ability to park right outside your unit if you have a car is very convenient. Even if you will be using the buses, there are enough bus stops so that you don't have to travel far to find one.