Oh geeze, I really seem to remember her making some comments about her mom, but it's all vague enough that I can't seem to Google up anything -- I really need to rewatch the first two seasons, too! It does make more sense that she'd have been on the front lines if she was fighting, at least, since for all that the Southern Tribes didn't have any problems with women bending, they don't seem to have any non-bending female warriors...

And the way the Gaang managed to pass off their quirks of appearance or misused slang as their being "colonials" really fits -- bits of the Earth Kingdom have been occupied for so long that there just have to have been intermarriages, and the FN equivalent of army/diplo-brats who were born and raised outside of their parents' home country...