Bag stolen at school - what can I do?

Well, what i would do is get somehing of equal enticingness, and in the same cl put it on the back of her chair. However she should tie some strinf to the bag and zip just in case and then tie it to her so if someone takes/opens it she will be alerted to it. Also allow someone like the headteacher knowledge of it, so it does seem to bad. Maybe tell the teacher you choice.