Head movement, glove swim, even FSR dont matter at all unless the arm is working the right way. Her arm does not work the right way. You should take her off the rubber and teach her to throw like the sticky IR in the classroom. You are putting the cart before the horse.
Excessive head movement is a result. The cause is underlying. I’m watching the video through a phone so the arm movement (whether IR or not) is tough to see. Hence my comments about what I can see.
Between the swim and the weak FSR the body pulls away from the throwing arm causing a lockout. It doesn’t have a chance to be loose.
I wonder if she’s in a stationary position that the arm action is better. Just food for thought.