Dead or alive, my conclusion (SPOILERS!!!)
So many people are discussing this, and some people say one thing and some say another. Some even bring out what the director says etc. etc..
But during all the arguments I missed one point, one thing that is so extremely obvious that nobody seems to have noticed it (including the characters in the movie!).
In movies where a character dies and his soul is portrayed, the same actor is of course used to portray the soul, simply because there isn't really any other way to portray a "soul". But of course an actor is a physically existing person, while a soul is not, so it goes without saying that this way of physically portraying a "soul" is purely symbolical.
So in many movies where a person's soul is portrayed they use a split screen or a body double. One actor would portray the person lying on the table and one would portray the "soul" so that you would essentially see the same person twice. The actor playing the corpse keeps lying still on the table and the actor playing the "soul" may move around the room, but he would not physically interact with any objects, since he isn't actually supposed to be physically present.
So, knowing this and having watched many movies like that, this movie was a little disappointing to me. Because if you watch the movie with this in mind there is really no twist and no suspense since it is obvious within the first few minutes what the "twist" is gonna be, simply by the fact that there was no body double lying on the table and that she was able to interact with objects.
If she was a "soul" why can she pick up a knife? Why can she trash the room? Why is the door an obstacle to her? It even goes so far that when she walks around, Eliot tries to get her back on the table so that he can continue preparing her body. If she was dead he wouldn't need to do that, since her physical body would have never left the table to begin with.
So if you look at it from this point of view, it is pretty obvious right from the very start that she isn't dead. And this also brings me to the problem I have with this movie. I think it's a great idea for a horror novel. This would work really great in a novel, but not on film. Because in a film they have basically no way to avoid this problem. So I can understand that this is unavoidable, so they have to use certain other cinematic techniques to distract the audience and lure the audience into thinking she might be dead.
But why does the character not realize it? Why does she need her breath reflecting on a mirror to realize that she is alive? Shouldn't it be obvious to her by the simple fact that she can still physically interact with objects?
But to answer the question if she is dead or not. Yes and no. She alive in a physical sense, but she is dead in the sense that she has lost her will to live and is extremely pessimistic (to the pint of mistaking her boyfriends proposal for a separation). And maybe that also kinda explains why she doesn't realize that she is alive and doesn't answer when her boyfriend knocks at the door to rescue her. She doesn't really want to be rescued - she WANTS to be dead.
So that is what Eliot means when he says that she is dead and why he regards her as dead to begin with, and I guess it is also the point of the movie.