Don't be so pessimistic Featherfall, I'm sure you'll find…. a book. Maybe not the book, but A book.

Pretty lil' library! One of my first experiments with drawing a room on my own. With references of course, but still…
I figured that now that Twilight's castle is no longer inhabited by Twilight, they'd probably want to turn it into some kind of study hall for the school or some kind of monument of Equestria, rather than making it a public library for all of Ponyville. Starlight still lives there too, so making her "house" open for the public would be strange. Plus she's the principal of the school now so it sorta makes sense.
So instead Twilight insisted on opening a new library in the center of Ponyville where books from all around the kingdoms would be collected and be accessible. Twilight of course donates some of her own books every now and then to this library to help encourage ponies to grab a book or two every now and then.