I get where you are coming from. However, this isn't like Miss Wallace is going to throw on her plate carrier and start clearing hallways while engaging hostile targets. Miss Wallace isn't going to be trained in close quarters combat tactics.
What Miss Wallace having a gun means is the final line of protection. That shooter actually enters Miss Wallace's classroom and is going to kill everyone in there. Miss Wallace, even though nervous and with some inaccuracy, has a chance to eliminate the threat. At the very least she has caused the shooter to change their current focus to the immediate threat that is Miss Wallace crouching in the corner with her 38. Even potentially causing the shooter to run from the classroom. A mass shooter is looking for easy targets.
But Miss Wallace doesn’t want this job. She wants to teach our children, not defend them from violence. That’s why she’s a teacher not a cop. The focus should be on putting her in situation where she doesn’t need a gun and can focus on teaching rather than expecting her to solve other problems created by societal failings.