She might enjoy the turtle farm, maybe there is a way you can visit Stingray City that she can do - a short glass bottom boat tour? They feed tarpon at The Wharf, which is touristy but has pretty good food and nice view for dining. When we went we were passing through overnight, on our way to Cayman Brac. Little Cayman had the best diving.
Grand Cayman was very much like Nassau in the Bahamas but with fewer historical buildings, more money and newer construction, safe and kind of boring, great weather, nice swimming and OK diving, $$$ drinks. The Sister Islands are very back-to-nature, less developed, underpopulated, with great diving and no nightlife. Little Cayman has a grass airstrip and 400 people. The reefs at Bloody Bay Wall were superb.