I also will bet money that there's something in the school contract she operates under that allows her to be terminated for behavior that brings discredit on the school district.
If there is no such clause, then the district will be forced to take her back, imho. They will have some process, though, for terminating employees, and this incident would be the beginning of the paper trail that will eventually result in that.
As I said, though, I'm betting they already have a behavior code for school employees.
As someone who dabbles in employment law, I can guarantee you that they would not have fired this woman if they didn't know they had solid grounds. Apparently they didn't even need a disciplinary hearing for this one. I'm sure that this is the functional equivalent of a serious safety violation in a nuclear plant.