Well . . . you can't cancel schools in the entire city every time some loon comes out of the woodwork. You'd never have school. And I have two kids at a DC HS.
Post armed guards wherever possible and hopefully they catch this idiot . . . or she suck starts the shotgun due to the publicity. Seems the perfect example for coming up with some kind of program where heavily vetted volunteers can be engaged to add the real (or potential) threat of a barrier to defective humans shooting up schools. I'd jump through some serious hoops to take a day or two off and add a layer. Maybe that's unrealistic thinking, but surely there's ways to beef up the security during certain times and at no cost to the schools.