right up until the day they're pushed to the brink and discover just how strong and powerful they are

Oh, for reals, me too. And obviously it's canon that Ursa was pretty damn ruthless when she had to be, and we do only see her through Zuko's rose-tinted memories and Azula's glass-o-conscience - I just can't dissociate my image of her from what we see there (hmm - not sure what this reveals about my general assumptions re wives n' mothers in fiction...). But I would love to read about Ursa: fearsome bender!