Originally Posted by
Alhuin
Naoi mentioned that Iwasawa disappeared, not because she was a "model student", but because she accepted her death, completed her dream, and moved on. If you look it at from that perspective... and take into account what Yuri said about why Naoi didn't disappear (beating "normal" students in the shadows), I think it it's safe to say that Kanade could be harboring some resentment for her death, or has not yet had her dream fulfilled (which I totally place my bet on being loved/having a friend, which Otonashi is steadily moving towards), so that's why she hasn't disappeared yet.