Watched Littlejohn warming up at the WCWS. When it came to her curve, she used a spinner first (had completely flat horizontal tight spin), then moved to a black full sized ball (weighted ball?), then a baseball, and finally a regular softball. She did about 10 reps of each at various distances.
Does the leap help get more spin on the ball? Ok, ok, just kidding.
She has amazing spin and control.