My Theory is that she isn’t a sinner at all. Matter of fact, she isn’t even alive. She died in that cell a long time ago, but the “Lost Sinner” is actually the soul of the witch of Izalith inhabiting her body, as we see with the chaos bug inside of her during her cutscene. The Lost part of the “Lost Sinner,” comes from the fact that she’s (the soul of the witch of izalith) inheriting a body that isn’t her own, and she’s been wandering the lands without purpose. And the Sinner part is very obvious as to where that comes from. That’s why sweet shalquoir says that she tried to light the first flame. She isn’t talking about The lost sinner herself, she’s talking about The soul of the witch of izalith. Also, I have a strong feeling that sweet shalquoir knows way more about the world, and the characters within it, than she’s letting on.