The problem was the idiot teacher was pushing the girl to use guns she couldn't handle and didn't follow proper gun safety procedures. It is very sad indeed, but this teacher became complacent and he not only ruined his own life, but also the life of this little girl. Now this poor girl will have to live with this tragic even the rest of her life that she took a man's life, even though it wasn't really her fault. Any person, regardless of age, should only handle a gun they can handle safely and strictly follow the rules of gun safety. Sadly, the teacher got carried away and didn't think this girl would ever pose any threat to him handling a heavy recoiling gun. She was too small, untrained and, IMO, young, to handle a sub-rifled type of gun like an Uzi, but the trainer just didn't care about it. A person with her limited training and smaller size should have started out with a 22LR rifle like a longer barreled Ruger 10/22 where should could have built up her skills with a gun that she could handle.
Such a shame all the way around.