It's still movement, her manifesting out of the dark: it's still a change. And change is what his eyes are looking for, and his goggles help filter the light.

He doesn't hesitate when she appears. He trains the scope on her and slams the light right onto her face in the same second. Hopefully it does what ADI said it would do, and pin the shade down. Even if it doesn't, it's a very bright light right in her face, so at the very least it ought to blind her and give him time to fire a regular bullet.

Which he will do in the next second, just in case. Might as well put a bullet through her forehead, if it'll do any good.