Hi! This is what I had in mind for Jo as far as Dean's game canon goes:
Eric Manner's (Bobby Singer's) step-daughter. A few years younger than Ford and had a crush on him for a long time. He slept with her a handful of years ago in a drunken moment of weakness and he regrets hurting her, but just looks at her as a friend. This is just what I had written up in case a Jo never apped. I'm open to working this out differently, though I would like her to be Eric's step-daughter, unless you're just super opposed to it.
I have that Eric (Bobby) died a few months ago in an accident at the automotive shop that he and Ford ran together. I haven't said whether or not Ellen was alive or dead, so that would be up to you! I would also be down for having Ford open up to Jo a little more these days, after Eric's death, maybe he even tried to sleep with her again and she shot him down?