I read some fiction on the internet that had a minor character girl who talked aloud to someone about how they flesh out the backstories of really minor characters, like the ones that say Welcome To Corneria, in the fanfiction that they write, with the implication that they've written a lot of fanfiction.
I think it was a webcomic in a cartoony / anime style, and that I would've read it a few, 2-3, years ago, but I reread archives frequently enough that it probably won't help.
I looked through TVTropes' list on their Most Fanfic Writers Are Girls and no character rings a bell, at least.
