Q: My daughters are getting a dead ball, not the nice backspin you recommend. What can be done?
A: If they hold the ball with the wrist cocked back (just by the weight of the ball) and then they straighten the arm in an upward action (a pushing motion) with a relaxed wrist and hand, the hand will flop forward and the ball will roll off the fingers with perfect backspin. My guess is that they are "doing" something with the wrist and hand, trying to wrist flip or snap the wrists, as perhaps they were coached to do. (Also the grip needs to have a little "finger pad" pressure to give them good control of the ball.)
Have them start with no ball and do the motion. See if the hand bounces when they extend the arm quickly (about 70-75% of max. speed and force). If the hand does not bounce, that means there's tension which is interfering with the natural backspin that will happen. Do it until the wrist is totally relaxed. Then add a ball and they'll get the same action.
As they shoot they will straighten the arm quickly, relax the wrist and hand totally and the hand and fingers will move forward leaving the ball to roll off the fingers with medium backspin.