Due to her mother's role as the keeper of Box Five, Meg occasionally acts as a source of information about the ghost to the other ballet girls.
Madame Giry is compelled to work for the Phantom because he left her a letter that told her that Meg (should she deserve it) would become Empress.
Early in the novel, it is explained in the Prologue that Meg Giry, after the story's events, had indeed become the Baroness de Castelot-Barbezac.
In Susan Kay's novel Phantom, she is mentioned briefly through Erik’s point of view; as she is telling Christine of the Opera Ghost he listens to her story.
At the end of the musical, Meg finds the Phantom's mask that he had used to cover his disfigured face resting on his chair in his abandoned underground lair, and holds it.
After being disregarded by The Phantom and feeling unappreciated by her mother, she kidnaps Christine's child, Gustav, and threatens to kill him.
A grieving, suicidal Meg goes on to rant about being used and cast aside then brings the gun to her head before accidentally shooting Christine and fleeing the scene.