random question since you are experimenting with your DD's IR like I am... lol... If she cradles it, which way is her hand facing coming out of the glove? the more traditional backswing, which way is her hand facing? My DD is trying to keep her back swing with palm to the catcher on the backswing (not cupping), with as quick of a 'short circle' possible, which has increased her spin and movement. It seems the external cue of make it spin has helped her create her own movement.Full disclosure the only person i have 'taught' is my DD. I suppose i have also 'taught' myself, but more to learn to teach DD.
That being said, I don't 'teach' the rollover because it is not possible. I was stating (or my understanding of what i thought Sluggers was trying to say or show) that the drill was a 'feel' to get the student to IR faster and get to the proper release location. If you try to do the 'rollover' drill, you will feel your hand have to IR faster to get to the correct release point. In my opinion it is more a cue of what to try and feel though it is in no way possible to ever achieve.
I believe that people who actually think it happens are wrong and their teaching methods are flawed because of it, but in this example because the 'cue' gets the IR done sooner, this incorrect teaching of what the pitcher is doing is actually erroring into a correct pitch.
I think i have stated before, i used the cue with my DD to start IR at 9 oclock. This was to try and get her a better change up, but turned out to be a better drop ball. My change up cue is bad, but used for a drop worked. haha. again, i dont know what i dont know. trial and error. and sometimes better to be lucky than good. I like knowing what actually happens, and then how to translate to DD is another issue all together.