@selfconfessedcynic: Yep, I was confused as to why they would design a Persona that doesn't appear in the game, so I did some looking and found out that she was the ultimate Aeon arcana Persona.
Still, it's weird how the end credits imply it's her Persona. I mean, they didn't really have to make a transition to a Persona from Marie, right?
...Marie can use ziodyne in the real world without summoning a persona, and this is your problem? Maybe she'll be a dlc character down the line for Arena since nothing in Golden contradicts it being possible.