That book Sarah is reading is Storm Front, the first book of The Dresden Files series. It's not a series I would recommend to everyone, and I would say it's definitely for grown up audiences, but I'm a big fan of the series. I particularly like the audiobooks that are read by James Marsters, aka that guy who played Spike on Buffy The Vampire Slayer.
Figuring out how to explain Sarah's spell was tricky. I've already shown it in action and had Sarah say stuff about it, so it wasn't just a matter of summarizing it. It was a matter of explaining it in a way that everyone who's found it confusing so far would understand. As I've mentioned, there are at least two reasons I want to make sure people understand the basics of how this spell works, so I really want to make it clear.
In any case, imagine how much reading Sarah could get done!