I think the books did deal with it better. Sookie thinks about her grandmother all the time at first, and repeatedly in later books. She remembers her when she makes changes to the house (or when other people destroy parts of it!) and when she moves into the master bedroom.

On the show, I didn't single out Sookie as forgetting about her grandmother; it felt like someone dropped her through an oubliette and out of the story. (I didn't like that on Babylon 5, either, where plain Word of God was that there was an oubliette for each character.)