The principal had the guts to give her life to protect her kids shows me that the answer, IMHO, should be a qualified YES. Let's be realistic...not every teacher/staff member is/would be willing to do that. To them, I say fine! To the others, I say great, go for it!!!!! Also, turning "Gun Free Zones" into "May Carry" zones adds to the deterent factor.
JMHOFWIW
Richard
PS: FWIW I have a BS degree in Elementary Education and taught for a time.