At 12, pop times are going to vary so much as girls hit their growth "spurts" a differing ages. I have seen 12 year olds that looked a 8 and that have looked 17. I generally focus more on using correct throwing mechanics and getting a baseline velocity and/or pop time on the individual catcher and challenge them to improve on their baseline.
Really good info, thank you very much. My DD is just finishing her first year at 12U and struggles to throw out a steal of 2nd. But based on her POP times (average 2.4) she certainly isn't too far off the mark. Pitcher's lack of velocity hurts a bit, which is exactly what I was trying to prove in my mind.
At 12U, you're only looking at about 0.1 seconds difference between a slow pitcher and a fast pitcher. 41 mph=0.58s to home. 50mph=0.48s to home. Most 12U pitchers will be in the upper 40mph range.
Since this is fastpitch and you can't leave until the ball is released, stolen bases are on the catcher, not the pitcher. In baseball, where they can lead off and take off early, the pitcher is definitely part of the equation.