In general, wheelchair accessible means manual and power wheelchairs.
The reason that some lines and accessible ride cars require guests with
ECVs to transfer is that ECVs are not as maneuverable as manual or power wheelchairs are. My daughter's manual and power wheelchairs both can turn in the the same space they are parked in. ECVs can't turn as sharply.
Manual or power wheelchairs that are no wider than 30 inches and no longer than 48 inches within the 'footprint' of the wheelchair space in accessible ride cars.
The specific attraction you mentioned, the AK Kilimanjaro Safari, won't be a problem. I can see from the picture that she travels on accessible transportation. The tram on the AK Safari uses the same kind of tiedown straps as buses and wheelchair accessible vans do, so she would use the same tiedown points on her wheelchair as she uses to travel at home.
The only other attraction I can think of offhand that uses tiedown straps is Toy Story Mania.
One that might be a little more difficult may be Ellen's Energy Adventure. That is an old ride car (? From when the park first opened). It has a narrower and shorter than average space and a steeper ramp than more modern ones. I don't know if they are allowing power wheelchair on there or not at this time. There was apparently a tipping incident at one point involving a power wheelchair and they only allowed manual wheelchairs after that.
Any attraction with a wheelchair accessible ride car has manual wheelchair available for guests who need to transfer.