I am glad you found the disABILITIES Board. I've thought of a few things we like to do that are relaxing.
1) Rent a pontoon boat at OKW or DD and take a relaxing boat trip. The boat channel goes from OKW to DD, or if you turn the other way, you can boat to Port Orleans. The pontoon boats are easy to drive and don't rock that much. We do this every time we go to OKW. It's about a one hour round trip from OKW to DD to PO and then back to OKW.
2) If you want to do a character meal, Crystal Palace in MK is a relaxing one. It's a buffet, so she would be more likely to find something she would feel like eating.
3) There is a porch at the back of the Boardwalk hotel where you can sit in nice wicker chairs or rocking chairs and watch the action on the Boardwalk. At BW, you can also rent surrey bikes to ride along the boardwalk. It's not necessary for everyone to pedal, so she might be able to do that.
4) You might want to look into an Illuminations Cruise (We haven't done one, but it sounds fun, relaxing and you don't have to fight any crowds).
5) Each park has some quiet places where you can sit and watch the world go by. Here are some of our favs:
MK: The porch on the Exibition Hall on Main Street (the building with Tony's Town Square Restaurant in it). Except in the early morning, it is shaded. There's a bathroom in the restaurant and a drink cart parked in front of you. The rocking chairs are comfortable. There is a ramp to get up to the porch (the part of the porch nearest the train station). It's also a great place to watch the parades and it's fun to watch people pose with the Goofy Statue below the porch.
Epcot: The eating area in front of the American Pavilion is nice, also the benches by the Rose Garden in the United Kingdom (lots of rose smelling there), inside the Living Seas and the tables inside the building where the Fountain View bakery is located (There is a pizza restaurant in there that is closed right now).
Studio:When it's not mealtime, the Commisary is a nice cool place to sit, also the tables by Anaheim Produce on Sunset Blvd.
AK: is kind of warm and there really aren't a lot of cool places to sit. One of the shows we liked was the Flights of Wonder in Asia. Every time we have gone, the CMs have been begging people to go, so it wouldn't be a long wait outside. The pavilion was outside, but shaded and fairly cool.
6) She can go to First Aid in any of the parks to rest. They are cool, dimly lit and relaxing with a cot to lie down on. Depending on where you are staying, this might be a better option than going back to your hotel room. A mid-day commute back to the hotel might involve a wait for the bus in the heat and a 10-25 minute bus ride. This can be very tiring.