I finally watched the episode this past weekend. Good theories! You know, when they talked about Jo being gone I totally blew it off and didn't even think it might be connected to the current case. But your idea makes a ton of sense. As for Ava, my guess was that she killed her boyfriend. In the beginning of the episode, the electro-kid was saying that the yellow eyed demon was telling him to kill people. So I just figured it finally worked on her. But who knows? You could be right. I liked her too, so I hope she's good. Sam and Dean need a girl on their team!