My thoughts are, we play to win.... we practice to get better. However, having a deeper roster is vital. So, I would absolutely let her pitch until the yips set in and then pull her for the better of the two. But bottom line is they both need the circle time to grow. If this kid was that fluid and natural, but lacked consistancy, she probably just needs taught about brushing...then you'd have an ace in no time. (Not that it would matter if her counterpart was the coaches kid)