The Exorcist and Christianity?

So here's the deal: I want to buy William Peter Blatty's the Exorcist (with my own money), but my mom sees that I want to buy it and she says "gross." She then goes on to say that "I don't even want that in my house." My mom is a christian and I think she remembers the movie when she thinks about The Exorcist. She seems to think this story is a demonic-worshiping something or other that shouldn't be read by any self-respecting christian. Is her remark completely ignorant? If you can give me some deep literary/critical ysis about the underlying theme of the book, it would be very much appreciated.