If Severian has a sister, who is it?

Question

During The Sword of the Lictor, protagonist Severian meets a little boy named Severian (see also Who is Little Severian?). Little Severian has a twin sister named Severa. This set of names seem to be given to twins, like another set of twins we meet, Agia and Agilus.

Is this a hint from Gene Wolfe that "big" Severian also has a twin sister? If so, who is it?

I have seen some theories online. Most seem to believe it's Merryn (a character I had to look up because I didn't remember who it was), and the WolfeWiki even says Wolfe has "confirmed this in the chat". What chat? Does anyone have a primary source for that confirmation?

If there is a Word of God on this topic, then why are there so many other theories around? Some think it's Valeria, others Jolenta. Which answer has the most basis in the text?

Answer 1

Yes, it's clearly a hint that Severian might have a sister, as it's explicit in the text:

"I'm Ava. Severian is one of these brother - sister names, isn't it? Severian and Severa. Do you have a sister?"

"I don't know. If I do, she's a witch."

Citadel of the Autarch, chapter X.

Merryn would fit straightforwardly because she is a witch; more elaborate theories are available.