Maggie is a student at St. Alphonso's Academy in Flint, Michigan.
She had been cast as "Sam Winchester" in the Supernatural musical. She is taken by the goddess Calliope because she didn't agree with Marie's out-of-the-box take on the story of Supernatural and was going to try to get the show shut down with the principal. Because Maggie is missing, the role of Sam is given to Marie. Maggie is saved from Calliope by Sam, Dean, and Marie.
Maggie also expressed a desire to do a play about Charmed, which Dean agreed would have been easier.