N.K.
I had the same issue as a kid. I was bullied and had things stolen. The way I resolved it was to put a lock on my backpack, so no one could open the pockets to steal my money or school supplies when I was standing in front of them in line. I told the teachers and they didn't care, I had bigger issues that the principal ignored, I am glad that teachers (seem to be) more proactive when it comes to these things, rather than sweeping it under the carpet and dismissing it as "kids being kids." I would try both the lock and having her report the thefts to her teacher, just in case the teacher doesn't follow through.