In this way, it is a quick, angry way of speaking. It is like an aligator that moves its mouth quick - SNAP is what we call the noise of a quick bite. Therefore Snap is talking aggressively.

Or it could mean that she literally snaps in half, so that one part of her body is in one place, and the other part is a couple of metres away in another place. Nice!

she snaps= she answers angrily