Well,I don't really know what to call that. Crime offence or a self defense. May be she is considering the life of the pupils around, and the life of her self too.

Though, here in Nigeria we have no right to take judgement in our hands, you can't kill someone just because you suspect he/she is a thief, even without concrete evidence. Your right is to hand him or her over to the police.

At the same time, there are some situations that warrants such a scenario and someone must make such of actions to prevent further damages.

There are things she can do as you said she is trained, she can shoot the thief at the leg or arm. At least that will prevent the thief from causing further dangers and will put her at less risk.

I first shocked when I first see "Mothers are dangerous " but I can see clearly now your reference.

Mothers are good ooo. Hahahaha
Thanks for sharing @reddust