IMHO, you should approach this problem from, "I want to make you a better pitcher." And then, show her how a good pitcher throws, and then work with her.
I have a nice frame-by-frame shot of Osterman throwing the ball you can use. There are also lots of videos available and pitch sequences you can use.
That is correct, except you left out the words "at release". After the pitch is thrown, some good pitchers do square up to the plate. It is the orientation of the hips at release that is important.
There is also an issue of "how open". Pitchers do close their hips somewhat prior to release. I've never seen even moderately accomplished female pitchers throw with the hips fully closed at release.
I read the articles Steve listed, and I didn't see this. Where are you getting this?
While Cat Osterman is a fabulous pitcher, she has her own very unique style to pitching that I would not necessarily use as the poster child for good pitching mechanics. At least three things she does which I would not emulate: a) she looks down at the ground, 2x, during her pitch (see Model Pitchers thread, page 2), b) she "hops" to stride plant, and c) immediatley after release, her pitching arm finishes in several different positions depending on the pitch thrown.
I would use Bill Hillhouse as an excellent example of proper pitching mechanics. If you are looking at elite female pitchers, Jennie Finch is a pretty good example of getting the hips open, long stride, and big arm circle. See the below link for a contrast in style between Cat and Jennie.
http://www.discussfastpitch.com/softball-pitching/5208-model-pitchers-3.html
By the way, pound for pound, Yukiko Ueno who throws 75+ is almost fully closed at release. Of course her body type (narrow hips) has a lot to do with being able to close her hips this much and not have her arm hit her right hip.
With regards to the Study, my takeway is that you shoudn't close your hips too early or too late before release, but definitely should close the hips somewhat to reduce the risk of injury.