OP I got a response from the Principal last night.
Thanks for including me in this email. I will talk with TEACHER tomorrow and we will address this with the class. I am sorry this has happened to DD.
I'm very pleased with his response and hopefully this doesn't occur again. I'll keep you posted with what he tells the class.
To address some questions.
The lockers do not have a locking mechanism. And her lunchbox is a cloth box so it doesn't have the capacity to be locked.
My daughter goes straight from my car into the school every morning. So basically as soon she enters the building her lunch box goes into her locker.
Also she decided she wants to buy a school lunch today.