The ending (again - SPOILERS)
So... She has blood on her face, suggesting that she really did kill her husband and her sister, so who is rattling the door handle? Or is the rattling door handle supposed to be in her mind too?
There are two constrasting realities there - either the blood should not be there, or the door handle should not be rattling... Either one of these is another hallucination or there is a third option I'm missing..?
Perhaps the film makers wanted to leave this ambiguous, but it comes across they weren't quite sure themselves. I did enjoy the journey of the film, even if it was quite predictable, but the destination was a bit frustrating.