Firstly, regardless of her age (or the success of the coach’s program) the execution of the depth jump is just horribly wrong. The simple rule is that you should always jump up at least as high as where you came from. Her jump over the hurdle is much lower than her position on the box, meaning that most of her potential energy is just absorbed and not utilized.
Secondly, jumps such as these are on the high end of our exercise inventory. If you use it at such an early training age already, you have lost the opportunity to introduce a new stimulus, a means of intensification, later in her career.