^ This.Quoting Wryan (view post)
"And what do we say to the god of death?"
"Not today."
Arya freaked out in the library and became more panicked as she tried to get away from the wights. The whole sequence was shot like a horror movie with her as the Final Girl.
Melisandre is basically telling her, "FFS, remember who are."
People are reading too much into the eye color thing. I took that as a callback to their first meeting. There's zero indication that she used a mask to sneak up on the Night King. (And anyway, what difference does it make?)