yeah, i agree. i am certain that she was not killing everyone. it makes no sense at all.
the creatures were there. i am not saying that she was sane either because clearly she had some issues. also, what the other women were saying about the creatures. why would they talk about their friend being numerous creatures?
the whole movie would not make sense if she were the killer.
These must have been people who watched High Tension and The Descent back-toback or something.