I think Amy is pretty much right.....her posture is not to bad.
You will note that after release she tends to "walk out".......this is an indication that she didn't get all the energy into the ball.....some stayed in the body. Front side resistance is important relative to the transfer of energy.
I cue phrase that works on many to develop front side resistance at time of release is "hit the wall and be tall".......do not let her step or lean thru the wall.
Hope that helps a bit.....she really is not to far off with her mechanics so this should be a relatively easy fix.