to elaborate, let's use the first 2 diagnostic criteria that the DSM-5 uses for Autism Spectrum Disorder:
1. deficits in social communication or social interaction
2. restricted or repetitive patterns of behavior, interests, or activities
1. deficits in social communication or social interaction
[ID: two gifs; in the first, Katara says emphatically, "I don't hate fun!", before putting Momo on her head. As Momo slides off she says, "See? Fun!". In the second, Zuko looks up from a war balloon furnace and says, "that's rough buddy." End ID.]
Both Katara and Zuko can be seen as having deficits in social interaction - whereas Zuko's difference in socializing is very obvious, Katara covers hers up by acting like a Mom Friend - or in autistic terms, she uses a mask. Masking is seen across the autism spectrum, but is seen more in women and AFAB people.
As with social communication, both are uh, lacking, in the jokes department:
[ID: two gifs; in the first, Katara says to Toph and Aang, "it's so hot...it's so hot, Momo is shedding like Appa! Huh? Huh?". In the second, Zuko sits by The Duke and Haru and says, "Okay, well, I can't remember how it starts, but the punchline is: 'leaf me alone, I'm bushed!'". In both gifs, their jokes are not well received. End ID.]
Both Zuko and Katara also experience trouble regulating strong emotions, leading to some of their social awkwardness. We also see both of them bend unconsciously when feeling strong emotions.
[ID: first, an image showing Zuko's meditation candles flaring as he receives bad news from Uncle Iroh; second, a gif showing Katara yelling at Sokka, and splitting open an iceberg with the force of her unconscious bending. End ID.]
Struggling to contain/regulate ones emotions is common across the autistic spectrum (and I can confirm as a person on the spectrum!). And while I'm sure we're all familiar with Zuko's emotional outbursts, Katara has emotional outbursts as well! Although she seems to have adapted ways to get her emotions under control quickly.
[ID: a gif zoomed on Katara, she has wide eyes and is yelling, "I'm completely calm!" End ID.]
2. restricted or repetitive patterns of behavior, interests, or activities
Both Zuko and Katara exhibit very rigid, black and white thinking. In Zuko's case, we see this in his obsession with honor and finding the avatar - with Katara, we see her rigidity in her rule-following/routine and strong internal moral code.
Katara's first fight with Toph is when Toph doesn't act according to the Gaang's established camping routine - Toph breaks Katara's routine, and Katara then reacts as seen above. Katara's second fight with Toph is when Toph runs a bunch of scams, which Katara both sees as morally wrong, and also likely to draw unwanted attention.
Katara shows us her strong internal moral code...all over the place. From going to save Aang, someone she didn't know very well who endangered her village, to refusing to learn bloodbending willingly, despite it being an incredibly powerful bending technique - Katara is governed by her personal morals.
So while her actions lead some to call her overbearing, controlling, or overemotional, I prefer to think of her as some of the best accidental representation of the Female Autism Phenotype in TV.
Katara is an autistic icon.
