I) Take her to the local water park. We get in free, but it's a mile away and I have no car.
II) Fill up her pool.
III) Take her to the beach. Last week she had fun in the sand, but the water was too cold for her. The beach is just a man-made beach, by a pond.
IV) Something else that I will suggest in the comments.
Parents, what are your favorite things to do outside with your little ones?