My Mom is 80, and we never stay in an elevator building. I always request 2nd floor. We've stayed on the 3rd floor before, and it is a little much for her, since she has had 3 hip surgeries. She does fine with a second floor room, though. If your mom is in good health, the stair probably won't be a problem, except for the luggage. If needed, you can always call bell services for help.
It also depends on whether you'll be driving and using your car during your stay. Ironically, the elevator buildings also seem to be the buildings with the most inconvenient parking spots.
The stairways ot OKW have a fairly gentle rise, and they have a half-flight, a landing, and a half-flight.
If you want to be close tot he restaurant, request to be near the "Hospitality House", that is the building that houses the front desk, and is adjacent to the restaurant, main pool, and a snack bar.