Because THIS is the Sookie from the books. THIS is the Sookie we’ve been waiting for. THIS is a KickAss Sookie that can (eventually) deserve Eric.
Not that I didn’t love this bit and the general Sookie-gets-a-clue nature of the episode, I don’t agree this is Sookie from the books. This is Sookie being cruel, seeking revenge, which isn’t the same thing as having a spine. The Sookie-from-the-books stands up for herself, gets a little hard, takes a dimmer view on the world, but I can’t remember her doing anything equivalent in the course of the books.
This is understandable inside the story arc, but I really did a wtf at the glee on her face.