Her name is Alice. She used to be the head of security at a secret underground facility for the evil Umbrella Corporation. The apocalypse outside? All those zombies and monsters trying to eat any human being left alive? Yeah, Umbrella did that.
The first couple of times, I chalked it up to character acting. You know, that snooty terminology used to describe, ah, acting. Giovanni Ribisi, I think, is a very good (character) actor. Dude can act.