The desire to throw with authority is in every student. The ability to do that is also in every student. The ability to bring all that out in a student is definitely NOT in every instructor.
Does she have a slight bend in the elbow all the way through the circle? If the arm is straight and the elbow is locked, she can speed up the arm with that little bend. It will also keep her from getting hurt.
Also, the arm 'circle' really isnt a circle. It's more like an oval as the body is moving forward. If the stride is strong enough and fast enough, it takes next to zero effort to bring the ball up to 12:00. A lot of folks havent fogured that out yet. The slower the stride, the harder it is to bring the ball up in front.
How strong and fast is her forward momentum / stride speed? That is probably your culprit that is holding her speed down.
So what you're telling us is that if a pitcher has the desire to throw that hard you can get ANY kid to throw 65 mph? All she has to do it want it and work for it. Sorry Hal, I just can't buy that. That is why the Finch's, Abbot's and Ueno's are tops in the world. Not many can hit those speeds consistently.
The same thing holds true for baseball. There are only a few who can hit that 100+mph mark and I'm sure these guys are getting the very best instruction there is out there.
Hal, I know I can get a pitcher's max potential out of a her if she's willing to work. But getting any more than her body is capable of is something that nature does play a part in.
I have two girls right now who are very similar in build and are about 6 months apart age-wise. The younger one is slightly thinner and out-throws the older one by a good margin. I've been working with both girls for the last two years using various drills to try and get the most out of them. Both work hard on their own time and want to pitch. Can someone else get more out of them?? Maybe... But I do know that every hard working kid I've worked with has gotten faster after spending time with me.