So.. I know the director states there's no possession, and I completely get that.
But... the One-Wish Willow's mechanics really raise the question, what the hell is going on then (pun not intended)? It's easy for us to handwave away the question for the sake of understanding the director's intent -- but think about it from a more critical standpoint.
There are many wishes that have happened, and clearly this story is a based around the Monkey's Paw which, while not directly demonic in itself, always carries with it unintended consequences.
Additionally, the phone call to the service number -- had that scene not been in the film, I'd be able to accept the director's answer on it's face. But that scene entails an external force is acting within the universe of the film.
I understand completely that's not what the movie is about; but the plot devices used to tell the broader narrative do seem to heavily borrow from and somewhat rely on the tropes of demonic possession stories and films.
I hate seeing people act like Nikki was "possessed" by some demon. She was overtaken by an obsessed personality that was created by Bear when he snapped the Willow. There's no demon, there's no Satan, it's just an ignorant entity born from the mind of a controlling man.