At 10u, 12u and even some 14u, kids are still growing, maturing and trying to figure things out on their own. I think the kid should get to hit if she wants to. Even though she might be the only pitcher I say let her decide if she wants to hit or not, after all she is giving you a chance to win if she is the only one that can pitch. I think coaches sometimes worry about winning to much and stop thinking about getting the girls better, I know I have at times. Everyone wants to win but somebody has to lose and if all us coaches cannot remember that then we all lose. Coaches are to try to help get kids better and my three steps to that are 1) you must learn how to lose and keep your heads held high, 2) once you learn how to lose you will then no how to compete and 3) once you learn how to compete you will then know how to win. This is just my thoughts