tldr; Noble girl wound up as a infernal sacrifice and the local church botched an effort to raise her, splitting her psyche and cementing her soul to an entity of pure hatred. She's kind of bitter about the whole thing and burned down the monastery where they were trying to cure her.
From the journal of Capt. Solverni Rue:
… In a cavern below the keep we found their victims, beaten and terrified but alive — all save one, Farahzad Eisale, eldest daughter of Tamil Eisale.
Crusader Alon, who studied with the church for years before becoming a knight, rushed forward and laid his hands upon the girl’s forehead, intoning a prayer of revival. And for a moment, we thought it had worked. The girl’s chest heaved with breath again, and her eyes flew open …
but inside her eyes was a void like the night sky. And then she screamed, and did not stop.
A letter from Brother Felis:
Farahzad has shown improvements in recent weeks; she no longer lies motionless in her room for hours — or worse, spends the daylight hours screaming as if in agony until she falls unconscious from exhaustion. This is a relief to the acolytes charged for her care, though they still find her unnerving.
But I persevered and endeavored to strike up conversations with her — not of her ordeal with the fallen, of course, but of happier things such as horseback riding or calliagraphy or dancing. The conversation turned to the church when a group of acolytes walked by on their way to the temple. The girl asked what the purpose of the temple was, and confused, I explained it was a commune with Mitra and look upon his aspects.
“But Mitra is the Sun,” she replied. “You should worship outside, staring up at the sun while you pray.” She pointed at the sun blazing straight above us. “Why don’t you do that now? Stare into Mitra and pray.”
More befuddled than ever, I explained that one cannot look directly at the sun’s radiance when she grew agitated and interrupted. “EXACTLY! Because you would be struck blind … Mitra blinds those who love him. He is the tyrant of the day. ”
She interrupted a funeral service yesterday, shouting at the mourners that there is no reward for the faithful, nor punishment for the wicked — not even the Boneyard where souls may be judged. “Mitra leaves us nothing! Nothing but the void!” she cried.
If an inquisitor were to overhear …
The next day, via a Sending spell:
The girl is a demon! I have locked her in her room. Summon Sir Balin quickly!
Report of Sir Balin:
My men and I were deployed to the St. Marcarius cloister upon the report of a demonic influence inside the sanitarium. When we arrived however, the campus was in the midst of a riot by patients, and two of the buildings were already burned. The chief illuminant, Brother Felis, and two others are thought to have perished in the blaze, may Mitra embrace their souls.
The one responsible is clear: Farahzad Eisale, the daughter of the Eisale family and a patient here. She was found inside the temple defacing Mita’s sunburst symbol with a black circle, beneath which was painted the slogan, “Put out the light.” The girl continued shouting those words to other patients as we carried her off, pointing first at the ruined temple, then at the sky itself.
I do not understand why these monks were so lenient with an obvious agent of corruption, but mercy was the wrong choice. She will face justice now.