So when I watched The Legend of Kora the grandaughter of Aang asked Katara what happened to the mother of Zuko wich Katara didn't get the answer because she was interrupted. I still don't know if Zuko's mother chose to go away, got killed, or maybe got forced away. I only saw the series I don't know if they explain in the manga.
This was answered in the Avatar comics, as you suspect. In particular, it was the second graphic novel released, The Search. The title refers to Zuko's search for his mother.
In the comic, everything about Fire Lord Azulon's death is revealed, as well as what happened to Zuko's mother, Ursa. I'll summarize here based on the wikipedia article and my own hazy memory. Ursa provided Ozai with a poison to kill Azulon, and after that succeeded, she was effectively banished by Ozai as a precaution. During her exile, Ursa got a spirit to change her face and erase her memories, married her childhood sweetheart whom she was engaged to before Ozai showed up, and had a daughter. During the course of the story, Zuko eventually finds his mother and her memories are restored.