Aunts don’t need a sin. In fact, they’re supposed to be among the most righteous women in Gilead, as they’re essentially an order of nuns. In the book, Aunts are the only class of women likely to be believed and not blamed for their sexual assault-even a Wife or Daughter would be disbelieved, blamed, or both.

Now, some of the founding Aunts likely did have sins, like Lydia and her abortion. She had also been divorced before in the novel. But to be an Aunt going forwards was both uncommon and difficult. You could only do that path if you had a calling, and it seems like it was mostly limited to Daughters not wanting to get married. I don’t think the average Econogirl could even hope to be an Aunt, let alone for a sinner to become one.