Jason Frank
In one universe, Jenny Everywhere once met the writer Jason Frank at a party in Brooklyn. They got to talking because Jenny was couch-crashing at “a friend of a friend's”, and Frank agreed to let her stay at his own place for a little while.
Jenny subsequently began imposing herself on Frank's life, notably convincing her to buy a scarf, goggles, and a better toaster. She also told him about the Multiverse and some of her adventures in it. Looking through the writing drafts he was working on (without his permission), Jenny ended up giving him actually quite helpful feedback. After she abruptly left, Frank realised he was going to miss her, and threw away his stalling drafts to work on a new story, based on one of the autobiographical stories Jenny had told him about one of her adventures. (COMIC: When Casting Calls)
Behind the scenes
The prose introduction of When Casting Calls, though featuring Jenny, is written in the first person by Jason Frank, who also scripted the comic. The implication is that the rest of the comic itself is the in-universe Frank's embellished rendition of the story Jenny told him during their cohabitation.