[The Squatter of Amon Rûdh]

Possibly because she kills the orc a couple of frames later. Look at her expression: she's waiting for her moment to attack something off-camera.

As for the stains on her hands, you don't have to kill someone to end up wearing blood. It could be from a wounded comrade or a freak nail-varnishing accident, but I think she's cut her knuckles on something. However it got there, there's plenty of blood to go around in a big battle: I'd be surprised if her hands were clean even before the first kill of the day.