Starlight has definitely exhibited some...unusual tendencies. Is she autistic? A sociopath? Some unknown. Pony-specific disorder? Her main issues seem to be difficulty relating to others, obsession with one subject (magic), difficulty adjusting to change (Sunburst's leaving, even leaving Twilight's tutelage.) Is Starlight autistic? Could explain why her papa treated her how he did.

If you read Unwell (which is actually about Twilight and predates Starlight by years) you’ll see she’s a textbook case of untreated Abstract Cutie Mark Syndrome.

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I can speak against her being a sociopath. She lost her only friend as a filly, and what does she call her villagers? Her friends. She very obviously feels things for other ponies. And from how she reacts when Twilight and her friends arrive, I think she believes she's genuinely doing these ponies a favor. If there's a condition for pinning the blame for personal hurt on the wrong thing and an inability to see past it, that's what Starlight has.

On a side note, I have a feeling the Christmas Carol episode recycled some of the old, discarded ideas for Starlight's past and backstory. It's just so similar that it can't be a coincidence.

"Then in that moment, though you didn't know it,
Your defenses set up walls you built to last
Leading to the pony you've become today.
And the spell you're about to cast,
It all comes from your past."