Oh my gosh - this was the obvious one and I totally forgot! Thank you for reminding me of that one and saying there was another track, I didn’t know that!
For FOP, just ask when you get to the part where they separate you into the lines to go into the first room - tell them you need the one with no stairs. When you come out, there is a walk way for wheelchairs and scooters that has no stairs - we use that every time.
For FOP, when you go down the stairs that take you into the store, there is a side route that is a ramp - you go left instead of heading down the stairs.
For Splash, there is a Cast Member that is about halfway through the queue just before the first flight of stairs - they can open a different entrance without stairs - it takes you to the exit side of the ride and they get you in that way.
I have the same problem and I used the handicap entrances. When you go to get in line you tell them you can’t do stairs and they guide you to the correct entrance. Sometimes if you are using the handicap and the ride doesn’t have a fast pass, they schedule a return time for you.
Disney is generally (in normal times…) very good at providing accommodations to anyone needing them. In contrast to Universal, for example. If she needs help and you ask for it you will most likely get it. I remember having this same problem with my group in our last trip. We knew DH52 had bad knees and feet, but it turned out that our DS11 was just developing a bad foot problem we didn’t know about and he was the one who couldn’t stand all the walking. I was shocked at how many stairs we had to go up and down at Universal. At Disney it wasn’t nearly as bad but there was just so much walking to get from one place to another. Previous trips there was a stroller so this wasn’t an issue with kids.