Hi, My Daughter, Who Is 15, Has One Side Of

Hi, my daughter, who is 15, has one side of her hip lock up on her periodically. It tightens up which makes it difficult for her to stand. She needs a few minutes to stand up then she has to basically pop the hip to stop the pain and get back to normal. This happens once every few days. She is an avid basketball player and never has pain running up and down the court. It happens after she has been resting or sitting for a while and has trouble getting up. We know its not snapping hip syndrome. Any help is greatly appreciated.