Did you have other theories about what the twist would be? (POSSIBLE SPOILERS)

So, if you already saw this, and hadn't read the book before, or even know that it was based on an already existing story (I'm clueless, I guess), did you have any theories on what the twist was actually going to be?

I thought in early scenes (when she was fighting with her husband in the hotel room while the kids were huddled together in the next room) that possibly it was all going to be tied to her "medical issue" and that maybe it going to all turn out to be a dream or some medically induced halluciation as she already lie dying in the hospital.

I had another theory later on when it was getting dark and they showed the fire, but for the life of me can't remember what that theory was. I think it might have had something to do with the water actually.

So, did you have any other theories? If so, what were they and why?