On page 63, they answered a question about her. Here's what they said:
"Is Azula really as evil as she seems? Or is there more to her?
Mike: As all the Avatar character, even Azula has a softer side, though it's buried very deep. As "The Beach" and "Sozin's Comet" showed she has a lot of unresolved issues with her mother. She really feels her mother didn't love her as much as Zuko, and this drives her crazy, literally.
Bryan: There are obviously truly evil people in the world, but in the case of Azula, her repressed emotions and jealousies corroded her spirit and made her become that way. It is possible that she could turned out better in a healthier environment, but growing up in royal family of nation seeking world domination proved to exacerbate her problems. But Zuko and Katara spared her life, and who knows she might have a chance to heal."