Not a problem. The tallest building on AC is three stories. They don't allow anything higher. Request 1st floor accomodations, and if she doesn't do well walking in sand, golf cart rental for a week is very reasonable. $180 to $250 per week. I don't recall any place with any stairs to speak of. Maybe two or three steps at best. She should be fine. Several places have pools with walk in steps. The swimming will be good for her. If she wants to snorkel, have her check out the boat first. Some are a little easier to board afterward than others.
She'll have a wonderful time.