The movie in France (Impressions de France) has a very nice, sit down theater.
The only shows I can think of where you stand for the whole show are the ones that Cheshire Figment noted. There are some other attactions that have a preshpow you must stand thru (usually aboout 5 minutes). The ones I can remember having a preshow like that are:
At MK:
Haunted Mansion, Tiki Room and Alien Encounter. Splash Mountain has a flight of stairs in part of the queque. They will probably not let her avoid these unless she has a wheelchair,
ecv or Guest Assistance Card (GAC).
At Epcot:
Test Track and Ellen's Energy Adventure. The American Adventure entrance into the theater includes either stairs or an escalator. They do have an elevator which wheelchair or ecv users ride to get up to the theater. They usually send guests up in the elevator 10 minutes or so before the show. Get there early for the show and request to use the elevator.
At the Studio:
Backlot Tour, Twilight Zone and Animation Tour.
At AK:
Dinosaur
Other things to think about:
Many of the shows in theaters "load" enough people to fill the theater into a "holding" area for 10 minutes or more while the show ahead of you finishes. That might be the preshow. Some of them have a limited number of benches where you can wait (like the Hall of Presidents), some have no seats (like Little Mermaid).
Many of the rides have moving walkways for boarding. If she is at all unsteady with these, she might be better off boarding at the wheelchair entry. For many rides, wheelchair and ecv users board at the exit. This allows extra room for baording, less people and the CMs there can often slow or even stop the moving walkway. She would need a wheelchair, ecv or a GAC to use the wheelchair entrances. Usually, wheelchair users wait in the regular line until close to the baording area, then they are directed to the wheelchair access area by the ride CMs.
