Mary should just ask if she could change her locker so that they will not know which locker is hers. She could also put something like a board in front of the locker so that the notes can’t get in. If she can, she can also hide a camera in front of her locker or anywhere else noone can see so she can see who is putting the notes in her locker. I have never had this kind of problem before so I guess im lucky.
