One of the animatronics the player is up against (she doesn't look like it in the picture, but just trust me on that). Outwardly, she's a very cold person who doesn't speak very much, and when she does, it's nothing that could fill out more than a line on a sheet of paper. 

For a description of her voice, she's always talking in a deadpan, almost robotic tone. I also imagine her not being the loudest. I wonder if it's as easy as I think it is.

Her speaking lines are very few and far between, actually; the only times she gets to talk are when she talks to the player after killing them a-la Ultimate Custom Night, and during the ending sequence of the game.