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In season 14 episode 10, Nihilism, when Micheal traps Dean in his own mind while possessing Dean, he creates a fake version of Pamela along with a bar in order to keep him there. However, isn't it strange that Pamela is there, and not someone else Dean had a stronger connection to? No. In season 5 episode 16, Dark Side of the Moon (Sam and Dean go to heaven), Dean has a conversation with Pamela that makes him start thinking about saying yes to Michael, even though he doesn't end up doing so in that season.
(PAMELA: Yeah, well, close enough. Look, Dean, I’m happy. I’m at peace.
DEAN: What? Are you trying to sell me a time share? I mean, what’s with the pitch?
PAMELA: (chuckling) I know that Michael wants to take you out for a test drive.
DEAN: (interrupting) Pamela…
PAMELA: Just saying. What happens if you play ball with them? Worst case.
DEAN: A lot of people die.
PAMELA: And then they come here. Is that really so bad? Look. Maybe… you don’t have to fight it so hard. That’s all I’m trying to say.)
Pamela tells him that it wouldn't be so bad if Dean let Michael possess him. I think this is why she is in his mind prison that Michael creates in season 14. She tried to convince Dean to say yes to Michael, and almost did, therefore causing Michael to use her as a trick.