Seeing ATLA pop up on my dash (specifically a post about Hama) reminded me of an old idea I had to explain why Hama only recently started murdering random Fire Nation people. Because it sure sounds like SOMETHING happened recently to make the change, rather than Hama moving around from place to place making people everywhere suffer.
Simply put: Hama had a family while hiding out in the Fire Nation territory. And then the family died because of the Fire Nation, underscoring the loss of family and community.
She found another survivor who escaped from a different prison. Hurt and traumatized, but alive. The other person was too scared to draw attention back to the Southern Water Tribe by heading home because what if what if what if someone else got home. Time passed as Hama and the Survivor found solace in each other; they don't have home but they have each other and that's enough given the journey home and safety there being too long and uncertain. (Maybe they eventually had kids? Whether they were drafted or fled, they're gone but hopefully alive.) The comb the Gaang finds is assembled from pieces each managed to hold onto - let's face it: the thing is HUGE for something supposedly hidden in her hair for years, and it'd be poetic if it was a whole remade from clutched fragments.
... and then one day a local boy from the village - one SO PROUD of the Fire Nation (so fearful not to be) - somehow realizes that Survivor is A Foreigner. Not the full extent of the truth, not even thinking that The Foreigner is dangerous in themselves or a spy or anything like that... just that somehow someone who "doesn't belong" is living in the Nation and there'd be trouble if anyone was found "harboring" them.
Local Boy was spoonfed propaganda until he choked on it, paranoid and fearful of any hint of Not Fire Nation / Perception of Treason and the problems that'd result if someone more volatile finds out.
So Local Boy abducts Survivor, ties up Survivor in a cave, and goes home panicking over what to do and how to solve the "problem". Survivor's trauma is back in full force over the imprisonment so they're blind to everything but the fear and the darkness. A week of misery results in their death.
Local Boy is panicking worse now. He doesn't think Hama knows what Survivor "really is", and is too scared to open up to friends or family. So he goes to the nice innkeeper who always has a smile for the kids and is so nice such a nice auntie that of course she'll know what to do.
Hama coaxes Local Boy to lead her to Survivor's cave. Sees what happened. And something in her breaks, but she's still smiling sweetly as she turns to Local Boy with assurances that she knows just what to do. And she does: Local Boy is the first victim of her revenge. Made to suffer exactly how Survivor suffered: fear, darkness, no water, no food, no idea if anyone is looking, not even Hama's presence to give some solace that he's not alone.
And then she turns on the rest. Hama has so much wasted time to make up for.
... but I thought the whole idea would be too bleak and struggled with workshopping the community and why no one would've suspected Hama if her spouse/livelong friend was the first to vanish.