I lived in Clearwater for a few years before moving to Orlando and have a few suggestions in addition to the time spent at the Aquarium.
You definitely will want to do more than visit Winter who is quite an attraction.

Caladesi Island in nearby Dunedin has a ferry boat that you can get on to take you over to a beautiful beach area. There is also some information on wildlife and the boat ride over is stunning. Many times the dolphins will jump in the water and play in the wake of the boat. The boat operators have been known to stop the boat and let passengers take photos. She can visit Winter and then see some real life dolphin playing in the water.

There is a nominal fee to get on the boat and you can rent chairs and umbrellas at the beach it self, or you can pack your own. There is a bit of a walk from the dock to the beach, but it is not horrible.
Here is the link to their site.
https://www.floridastateparks.org/park/Caladesi-Island
There is a wonderful pirate ship boat...
http://captmemo.com/ right there practically across the street from the aquarium so you would be closer. That is also a good way to see the dolphins playing!
Frenchys' restaraunt is a favorite of mine on the beach and also right in the area of where you will be.
Enjoy your trip to beautiful Clearwater Beach...probably 1 .5 hours but allow extra time for traffic and road construction on SR 60. LOTS of road crews and traffic. Not to mention the locals and tourists who love the beaches!
Tracey