Question About "The Last Exorcism"

As I recently saw this movie, I plan to write a review at some time. But first, I have a question about the plot that's bugging me. When Reverend Cotton Marcus asks where Nell is, the demon who is possessing her says "She's in the fire. She has been for some time." Does this mean that the Reverend did not ever interact with Nell throughout the film, and the demon spoke through her throughout the film? Interpretations needed.