OH WAIT. With more time for my very cursory googling of Naomi Novik + fanfic to percolate through my brain, I now have a strong hunch who in fandom she is. Because there were only so many people who were intimately involved with the founding of AO3...

(My mind is kind of blown, and in turn now I really want to blow my librarian colleague's mind re: the reason behind his complaints that the sorcerer in "Uprooted" came across way too much like Severus Snape...) ;-)