what can i do for a swollen leg for a minor?

My daughter has a painful swollen leg. I took her to the hospital and the took xrays of her knee, ankle and her leg, they also did some blood work and everything came out fine. Im very worry. I dont know what to do or what can it be. She doesn’t have a bruise n she didn’t fall. Can you please help me?
Thank you in advance

Put a pillow under her legs when lying down, which may lessen swelling related to the buildup of fluid. If she need to stand or sit for long periods, tell your little one to take frequent breaks and move around.

Cut down the salty and junk food.

Get her urine test done.

Also check any insect bite.