Even better than a movie go to a live musical or play. She will be certain to love that.
Another really good one is go to a lake where the rent sail boats. Even without experience you will be able to sail down wind. Getting stuck is half the fun. Then you get to show some muscle rowing back to the dock.
One time, at a beach in Cozumel Mexico, I dove repeatedly to the ocean bottom retrieving sea shells, sand dollars and coral to give to the lady I was with.
Another time for something really different, I took a date Parasailing. That was also in Cozumel. A bit of advice is make sure the tow boat has plenty of gas. And discuss with the tow boat pilot how you would rather go into the water than into a building or sailboat mast on the beach. Accidents are rare but this will eliminate even them.