Aye. Could be that her mind blocked much of her abilities from herself to protect itself. And I do have a character with a rather unusual form of Firebending (which some, in the 'outside world' could likely assume him related to Azula hint though he isn't).
Very intriguing concept... could be that Sunny teaches them, rather than feeding on negative emotions, to feed on positive ones or ambient ones... logically, they'd get far stronger (and potentially be able to boost each others' power through their, no pun intended, sisterhood).