Reality is a little bit messier than your fantasies.
Ideally.
As a side note, she shouldn't shoot for the head anyway, especially if the bullet is going to go propelling out of the man. That's a great way to have unintended collateral damage.
Uh, we're talking about people who are frequently suicidal and are mentally ill enough to shoot up a kindergarten. I suspect they're not weighing odds in a logical manner, somehow.