Yeah, pretty much the first thing we ever heard her say was her questioning Katara about Zuko's mum. It's hardly surprising that she knew about the library.
Anyone else think it's a little creepy that they just left the professor's body there to rot? Also, if you can't loose or gain weight in the spirit world, what exactly did he die of? Old age? Terminal case of irritated spirit owl? I know there's a difference between entering the spirit world physically and spiritually, but I'm still a little confused as to the rules.
Also, maybe it's asking too much what with three (two and a half?) characters from the old series returning, but I rather expected Hei Bai, Koh or even that lemur spirit to make an appearance.
Actually, I may be mis-remembering but didn't Koh also dwell is a gnarled, ancient looking tree like the one Vaatu was trapped in?