Any person who attempted that would be a felon, and the resisting of an attack by any felon in the act would be justified.
Absolutely, in my opinion. (Securely, of course.) But then, so should every other freedom-loving adult who desires to resist felonious actions that may arise in our lives. It's the entire point.
Take the number of sporting events you've ever attended. Many of us have probably witnessed a person go sideways, bring out a weapon, strike (or even badly beat/harm) another person. Yes, if weapons were brought by every upstanding person, there would be more weapons there. But that's exactly the point of the exercise: to make it absolutely impossible for a felon to gain the upper hand against upstanding citizens ... here, there, everywhere. Yes, situations would likely be shut down via firearms, then. But, they would be shut down, instead of leaving everyone with nothing to do but weep about their hollow inability to do a damned thing about it. And, at a place where our defenseless children are gathered? It's at just such places where we have the most reason to ensure things are safely protected.
In short: this woman sees clearly, thinks simply and acts accordingly. She is not a threat. Not by any standard.
Awesome post, I wish I could word things this well.