>>42274560
I don't really disagree with your assessment but I think these events correlate to a preexisting condition better than just abandonment (this being a writing issue is debatable, I don't really mind but still).
>she thought Trixie would abandon her if she showed any kind of displeasure
Someone completely inward thinking would be prone to not knowing if the person they're talking to hates them.
>she held extreme guilt over her past mistakes while literally having nightmares over her own perceived unworthiness of being forgiven
Yeah that would actually be the natural conclusion of disciplining someone that believed they were being rational. It's more like they're threatening her at that point and she goes along with it basically because Twilight said so.
>[...] Starlight's entire character is based on empathy
Those aspects could be interpreted as her trying to understand its function, especially if it caused inner conflict for her ("why did Sunburst leave?").

This would also explain her smug and megalomaniacal (outgoing) demeanor changing to a more closed one after her reformation. They didn't rehabilitate her they just made her obedient.

If she had social anxiety she would actively avoid talking to people, she never feels fear talking to others.