It's never stated WHERE she is. Zuko's mother was banished because of "terrible things" that result in Fire Lord Azulon's death. It's obvious that she killed him to prevent Zuko from being killed.

I hated that Aang and Katara got together. I knew it was going to happen but still. And she's like 14 so she's just a more mature child. I was a total Katara and Zuko supporter. I want more episodes.