I run a drill as an exercise so the girls have "balance", especially in their spin pitches. Keeping the weight back is realistically only for the riseball and to explain would take too much typing for me today. I named the drill the "flamingo" and to be honest I did not come up with it myself. Coach Kempf uses it in her pitching lessons. Start out on the pitching rubber with the push off foot turned to about a 45 degree angle. Stand on that leg alone and raise the other off the ground so the toe is about even with the top of her shoe and behind her stationary leg. Now you'll look like a Flamingo bird. Point your glove to your catcher, arm spin, wrist snap release, while moving forward and get your landing foot to now go to the ground in her landing zone and bring the push off foot forward and finish with the push off foot now off the ground and in the air behind the landing leg. You should finish with balance and again be on one leg simulating the look of a flamingo but on your other leg. Setting up with the push off foot to a 45 degree will help you establish the proper shoulder angle for you to arm spin the pitch towards the target. the movement forward will have the trailing push off foot with the toe pointing downward and in dirt normally leaves a mark like a snake has been crawling on the ground behind her from the toe dragging.
This completes the exchange of the body momentum going forward, keeps the girl upright and standing tall, and finishes with balance. If they can do this drill they can throw most of their pitches with control. They'll get the rest of it once their confidence gets better.