Hi and

to disABILITIES!
I have two suggestions for discussions with your mother.
One is pick a point about a mile from where she lives. (This is something I did with my mother when she was only 91.) Ask her if she could walk there. If her response is something as "I could if I had to", then ask her about walking there and back four times. Eight miles is a typical day walking at WDW (once around the World Showcase Lagoon is 1¼ miles).
Then, ask her the following questions. Here are the suggested answers to go with them.
1. Are you disabled (even temporarily)? Yes.
2. Do the people you are traveling with, such as your family, know you are disabled? Yes.
3. Do you expect to meet anyone you know during this trip who may not know you are disabled. Probably No!
4. Do you expect to meet a bunch of people who you will probably never meet again in your life? Probably yes!
5. Is there any reason at all that you should care what these people think about you? Absolutely No!!
6. Will using a wheelchair or
ECV make for a better vacation for you
and your family? Absolutely YES!
Also, the Guest Assistance Card (described in Post #3 of the disABILITIES FAQ) states specifically on it that it is not intended to shorten the wait for attractions. All of the attractions at AK and DHS are mainstreamed, as well as almost all the Epcot attractions and many of the MK ones. There are a few where as you get close to the load area you will be pulled off to a separate line to avoid stairs.
However, a key to everything is that disabled access tends to take longer than the regular line.