Madame Giry is compelled to work for the Phantom because he left her a letter that told her that Meg would become Empress. Early in the novel, it is explained in the Prologue that Meg Giry, after the story's events, had became the Baroness de Barbazac. "Never you mind how I know I just do that’s all. We know a lot about the Opera Ghost, Ma and I, but it isn’t safe to talk about it here. And you’d better believe me for your own good- he doesn’t like people who don’t know how to show a proper respect, and when he’s angry terrible things happen.” “What sort of things?” I heard real alarm enter the other voice now. “Awful things!” said Meg cheerfully, “truly awful. The floor in our dressing room starts to run with blood...” Up in box five I blinked in surprised amusement. That was a new one! Little Giry should be writing Gothic novels, not prancing around the stage dressed as a water nymph!"
In the movie/play she is portrayed as having blonde hair and a healthy golden complexion. Meg was portrayed by Janet Devenish in Andrew Lloyd Webber's musical, and by Jennifer Ellison in the 2004 movie The Phantom of the Opera.
In the musical, Meg is the one who suggests to the theatre managers to put Christine in the leading role of the opera Hannibal once leading lady Carlotta Giudicelli is spooked by the Phantom's threats. Normally she and Christine would be part of the ballet ensemble led by Madame Giry. At the end of Christine's performance, Christine confides in Meg in the musical number "Angel of Music" that she has been coached by a mysterious tutor who is calling her to him. Meg dismisses her claims, but after Christine's disappearance, comes to believe in the Phantom's powers, in part due to her mother's experiences with the Phantom as a young man.
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.