くる at the end of the sentence is a subsidiary verb which describes a motion coming toward a "main person". Since this story is written from the first-person view (俺, 僕, ...), this くる probably means ナイフ is coming toward the first person narrator. That is, although "she is motionless", she is at least slowly moving her legs.
Nevertheless, as @NicolasLouisGuillemot points out, the biggest hint should be in the story itself. Who is holding the knife in this context, after all? How many people are there in this scene? It's difficult to say something with confidence from only those two sentences.