We don't know yet - a graphic novel will be released this upcoming september detailing exactly what happened. All we know is that she suspiciously vanished while Zuko and Azula were children the same night that Fire Lord Azulon was killed died.
4. Which two people save Sokka's father and Suki from the Boiling Rock?
I did quite specifically request it be spelled as it is on Avatar Extras. emotion_awesome
I wasn't expecting the Avatar extras to have a typo. emotion_awesome
It's spelled Kaya on Avatar Extras. .___. I'm not really sure where Kya came from.
That's how it's spelled pretty much everywhere else, like in the credits of the one episode where she has spoken lines. It's also how it's spelled in reference to Aang and Katara's daughter. It's also what Katara's name was originally supposed to be - they changed it because it came out so close in proximity to a video game whose main character was named Kya and they didn't want to be accused of copyright issues.