Maybe she could offer to settle by screening Miracle on 34th Street for the class, and she’ll provide the popcorn.
Yeah, it’s clearly a ridiculous suit to any rational adult – and how she can sue the mother is beyond me – but if kids can be suspended from school for biting a Pop Tart™ “in the shape of a gun”, or pointing a finger at a child and saying, “Bang!” (without a clear and immediate threat involved, which might take on different meanings in a high school setting, for example) it’s clear that common rules of rationality do not apply to public schools and the inmates thereof.
It will be interesting to see how this plays out; I do not have much faith in a sensible outcome.