[TOMT][Book] Book about fae and supernatural

I am trying to remember a book I read over a decade ago at this point. From what I remember, it starts off with a woman realizing she's being kidnapped by a serial killer in the wrong taxi. She causes a car accident and kills it, and it turns out to have been a dark fae. The fae he killed's power goes into her and she passes out.

I remember her meeting an elderly couple who gave her a ring to travel between the supernatural and human world. She had a friend who was a monster under the bed. And had to travel through the supernatural world for something, just can't remember what.

Also there was some kind of help line she was able to call, like magic IT or something.