Hand size may be problematic as well. My dd has pretty big hands, but even so, she really had trouble gripping the 12" ball when she moved up from the 10" She tried out for pitcher with the 12U team she played for and was not taken as a P, though she still made the team. By the time the season rolled around, however, she had grown enough that she could grip the ball correctly and was back to throwing with good velocity. She ended up not pitching for her 12U team that year. But, she stuck with it and is now back to pitching for her current 12U team as well as for her school team.
Edit: Now the problem is her hips... they're getting in the way where they did not before. lol