<p>Quelana is known to have passed her knowledge of pyromancy to only one other person:
Salaman the Master Pyromancer. The problem with the theory that Quelana is the Lost Sinner, is that there is no evidence that she was even still alive, much less that she aqcuired the Lord Soul of Fire (because that is precisely what it is), found her way to Drangleic, someone how got taken control of by the Bed of Chaos larvae (which would've died with the Witch of Izalith once they were slain), and somehow gotten close enough to the First Flame to attempt to rekindle it, even though it was locked away in the Throne of Want that no one but Vendrick would've been able to access. There's too much supposition to the theory and not enough actual evidence. However, there is plenty of evidence to hint at the Lost Sinner having the Witch of Izalith's soul, espeically since the DLC has pretty much come out to say that the theory of cycles of Ages of Fire is a fact, and that the four Great Souls (that would be Gwyn, Nito, Seathe, and the Witch of Izalith) reappear at the waning of every cycle. If you want to claim that Quelana somehow found her mother's soul and took it as her own, there's nothing that would discredit it. But by that logic, there's also nothing to discredit that Vendrick somehow obtained the Covenant of Artorias, and now has the ability to traverse the Abyss.
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