IMO, a 9yo girl has no place firing a full auto weapon, nor a boy that age for that matter. At that age, they need to be working on fundamentals and above all, safety. They need .22's at that age, maybe a single shot 20ga. That's what I had. Depending on maturity and evolution with what they started with, perhaps they can move up to an AR when they hit puberty --but it belongs to the dad of course, supervised use. And still, even at that age, they should be working on fundamentals still, maybe competing, maybe being introduced to their first high power.
Full auto is icing on the cake, as it were. Why give icing to a kid who hasn't even eaten his/her vegetables yet!
There are adults that can't handle that weapon, I bet my wife couldn't properly, but more over that weapon is a mini-Uzi (not the micro) if the pictures are correct and it does have much less weight and fires at a higher rpm than the regular Uzi, which MAY have been slightly more appropriate, if giving a child a full auto weapon is appropriate at all. I seriously doubt a 9yo girl simply has the strength to control such a weapon. That's really the bottom line I guess. Serious doubts about her ability to control it should have been raised.
There are two reasons for firing a full auto weapon in my view. One is for fun. Fun for seasoned, practiced and older firearms owners. Not for young kids. Then the other reason is to learn how to lay down suppressive fire or take or maintain fire superiority, and in certain instances, shooting on the move and clearing spaces. Generally military shit that 9yo's have no need to concern themselves with. It just gets in the way of the fundamentals they should be learning.
I really feel for the girl, I'm sure this has traumatized her greatly. I feel for the instructor's family too, but I wonder how he was brought up to think that was okay? Perhaps he was just trying to show kids that these aren't all evil so they'll know the truth when they grow up to vote? I've shown off my AR's with a suppressor before for that reason, to dispel the myths (to anti type grownups though).