Is there some basis for the "knee up follow through" that I don't understand?
My guess would be trying to train the pitcher to avoid dragging their push leg like a boat anchor...
At LSU we call this drill one-to-one, as in starting with your drive leg up and ending with your drag leg up. This drill is done from mound distance and it's to fire out with your backside and get out as far as you can in your stride without using any negative movement to start. Our drag leg finishes up to work on getting knee to knee in your finish & being able to finish balanced. This drill is in my daily collection of everydays.
1) She has to fix the front side resistance ASAP. Do walkthroughs at normal distance. After she throws the ball, she is not to let her right foot come down until after you return the ball to her. Don't be in a hurry to throw it back to her. She fixes her front side resistance, and she is going to gain 2 or 3 MPH. (Your DD was doing walk throughs 3 years ago to improve her arm strength. At her ability level, distance throwing is not particularly helpful.)
I think it is just the result of bad mechanics. Leapin' lizards that is one bad IP Batman!