Sorry to hear.
We took my mom on a last trip before she died of colon cancer a few years ago. We pushed her in a wheelchair (we are used to traveling with our daughter who has cerebral palsy and uses a wheelchair, so pushing another wheelchair was no big deal to us).
A couple things to add to the advice from lanejudy:
1) Plan your day based on when she’s usually at her best. For some people, that’s first thing in the morning. For others, they need a few hours to stretch, chill out, rest from getting ready before they have the energy to be out for the day.
2) Let her know that you can stop and rest whoever she (or anyone else) needs to - try to keep your planning fluid so there is no worry about missing planned events. If she’s tired enough that she needs to lie down for a while, each park has a First Aid station - just let them know what you need.
3) If she’s unsteady and/or needs assistance in the restroom, each park has Companion Restrooms. They are single stall restrooms with a toilet, sink and enough space for a wheelchair and someone to assist. They are marked on the park maps for Guests with Disabilities, which you can pick up a the park map kiosks or from Guest Relations.
4) Guests can get free ice water from any quick service restaurant just by asking. You might want to check out menus for the different restaurants - in order to do it on My Disney Experience app, you need to ‘pretend’ to be Mobile Ordering, then the menu will show up.
Mobile Ordering is a good way to shorten your wait in line for food. Some of the places won’t let you in to sit at a table until you have your order.
5) If she’s better with small snacks or foods she’s familiar with, you can carry in food or drink - just not in glass.
6) The effort of getting in and out of ride cars adds up. With my daughter, we try to not do too many ‘must transfer’ rides in a row. We alternate them with shows or attractions where she can stay in her wheelchair. There are not a lot of attractions with wheelchair accessible ride cars, but each park has some. Posts 18-22 of the disABILITIES FAQs thread has more info - see the posts stuck to the top of the board or follow the link in my signature.
7) Plan ahead what she wants to do. In my mom’s case, she just wanted to go to EPCOT, not even to go on any rides. We bought her a one day ticket, but could have added additional day(s) as long as we did it before leaving the park on the day the ticket was used. It’s a bit more complicated now with needing to have park reservations, but still might be doable.
8) Expect that she might get tired all of a sudden. Even sitting up in a wheelchair can be exhausting for someone with little energy reserve. If she needs to go back to the room, she may need to rest in First Aid to have enough energy for the trip back to your resort. Plan ahead who will go back with her - some people are worried about ‘spoiling everyone else’s fun’ and would do better knowing what will happen if they need to leave or rest.
I’ll post more if I think of more