I have posted before about a 'small ball-circle drill. Very similar to what is in the video but instead of an internal cue using the elbow I prefer an external cue which uses the ball itself. So I tell the pitcher to pay attention to the ball in the circle, and make the circle smaller. In order to make the circle smaller she has to bend the elbow. We start with a very small circle and just experiment with it.
Talking about shoulder movement. This pitcher controls the shoulder perfectly, it’s easy to be short because her arm action isn’t effected by a long arm action. The circle and the shoulder is stable, short. She starts with the shoulder forward and the lowerbody works underneath (pelvis movement included).