There will be a bit more on that coming up next story, but in short from previous stories: Faite was human once, but she became almost non-human from not living among them for several hundred years. After the whole Parody Master thing, she decided she needed to be closer to the people she was supposed to help, so she reinvented herself as a teenager.

Why a teenager? Because it's the path of least resistance. Society will always take care of a kid, but not an adult. And a teen rather than a child because if she went too young she would lose the mental capacity to do much of what she needed to.