There are some people whose physiology is simply set up to have speed. Check on what Ty Stofflet had going for him, regards height, arm length, strength, etc.
jim
jim
One of the most primary and essential components involved in generating consistent speed is the wrist snap. Think for a moment about the primary mechanical difference between a fastball and a change-up. One is not supposed to slow her arm down or change her leg drive for a change up. This would result in "broadcasting" the pitch. Therefore, just by removing the snap or creating a slow backspin, we are removing ten to fifteen miles per hour. If speed is inconsistent, start working with a spinner or some snap drills to make a full range-of-motion wrist snap as natural as breathing.
After mastering the snap, a long and fluid arm circle is necessary. Arm speed is wonderful as long as the arm circle stays on a line towards the target. I have seen some girls try to throw their hearts out, but as soon as that circle shortens up substantially or goes offline, it becomes increasingly difficult to generate speed and power. Younger girls are especially prone to this type of problem.
Leg drive can add an amazing amount of speed as long as it is executed correctly. The plant leg should be at forty-five degrees and on a line extending from the push leg. The push leg must maintain contact with the ground but come as far from the pitching rubber as possible while the plant leg is still in the air. The drag should be forceful and not come out too far behind the body. The drag leg should basically support the action of the wrist and follow-through.
Once you are absolutely certain that your daughter is doing a mechanically sound pitch, she can probably start doing some power drills (or speed drills). These will help her to move her body faster once she has sound mechanical execution. There are many different speed drills (throw and run, double circles, etc.), but you will probably have to experiment to find the ones that produce the best results for her. Good luck!
Secrets of the Diamond
If I am correct that there is a window of opportunity for developing fundamental pitching skills that closes on a kid at the ripe old age of early teens, then we have no time to waste.
If my memory serves me correctly, Michelle Smith started pitching when she was a sophomore in HS.
I would argue that this is the exception, not the rule. Had she been practicing and game tested since 8U, I have to believe these experiences would have made her an even better pitcher by the time she reached college than pickng up pitching in high school.