I think it's the potential for harm that makes her punishment somewhat justified. Not unlike charging someone for driving drunk, when they haven't actually run anyone over yet.

I knew a guy in high school that got expelled in the middle of his senior year, because cops turned up an airsoft gun in the trunk of his car after they brought drug dogs through our school parking lot (this was done routinely, inside the school and also in the parking lot, probably still is). That to me is a much worse example of how far these "zero-tolerance" polices get taken.