Well obviously somthing in her would have snapped to make her do this in the first place, maybe it also caused a split personality, when they showed the carver coming in it was just in her head. If they reveal it as her and they do one of those little flashback things to put all the ieces together they can show her there looking at the Carver only to show that no one else is there..or maybe she's looking in a mirror, and they can show her carving her own face....
but anyway, can't bloody wait for the finale!