This over-under trick could dramatically improve your pitching motion and it is so simple, I don't even need to make a video!
When you bend you knees to begin your push, you need to have your knees OVER your toes. It is very common for females to collapse their knees inward in squat positions. Practice this in front of a mirror and add 30-50 body weight squats to your daily workout.
Finish with your drive leg, UNDER your body. Right handed pitchers should have your right leg under you and left handed pitchers should have their left leg under. Sounds pretty simple but this is the most common mistake I see in pitchers.
The reason most pitchers forget these very simple mechanical motions is that their legs are not conditioned properly and weak core muscles. Get a jump rope, start running, and start doing lunges. Your team can only go as far as your legs can take them.