Have her and her teammates work standing vertical jumps from an 8 inch safety mat or landing mat upward to a resi or stack of some sort. Since the resi will require a bit of a forward jump, and defeat some of the purpose, you could try having a spare bar (yeah right) set at a height that works for the shorties so they can jump from the safety mat to a hang on the bar. Raise the bar for the next group once they've had about 15 jumps. Repeat until all the kids have gotten their jumping done.
Just to be on the safe side set the first two sessions up as a teaching/learning experience because grabbing at their fingertips when first learning how to grab can cause problems through the entire length of their arms.
I think the biggest benefit is the way the mat's soft surface slows down the jump to give them a chance to figure out the twitch sequences, movements, and forces that make a good jump work. Strength??? Probably not so much.... but some helps.