Kitty Norville, based on the title, is the character who is going to save the world. She could be a normal person thrust into extraordinary circumstances, or perhaps she has some pre - existing skills or knowledge that make her the ideal candidate for this world - saving task. We can't know for sure without reading the book, but she's clearly the focus.
Definitely not. 'The Exorcist Believer' is a work of imagination. It doesn't have any roots in actual happenings. It's all about crafting a captivating and spooky tale.