I think that's an interesting idea for a lesson, especially since students struggle a little with direct vs. indirect quotations. On the other hand, the "Twilight" series is one of the worst series ever written, and I don't know that I could condone its use in a class that teaches good writing. :-) Still, I think it could be cool to show that to students and encourage them to make up their own mini grammar lesson using characters and situations from a book that they like, or maybe from a book they were all using in class.
Speaking of "Twilight," I very much enjoy this site. It picks apart all of Stephenie Meyers' bad writing (grammar, run-ons, etc.) It is geared for [snarky] native speakers, but I think our students could gain something from it...like, why clear, concise writing is important!
http://reasoningwithvampires.tumblr.com/