Butter knifes are the gateway knife.
Pretty soon, she'll start bringing in paring knifes, then she'll move up to steak knifes, and before you know it she'll be toting a K-Bar in her backpack.
From there, things will only get worse, as she moves on to other edged weapons (cleavers, axes, scythes) and eventually works her way up to projectile weapons and biological agents.
Can't you people see the progression? It's so damn obvious a blind man could see it.