Madeleine and Jocelyn were close friends in their youth during their schooling in Alicante. As Madeleine had always seen Valentine Morgenstern as selfish and hateful, she always knew what kind of man Valentine was going to be, and had tried to dissuade her friend from marrying him, insisting that his charming demeanor masked a terrible amorality. While Jocelyn had convinced herself that Madeleine was merely jealous, Madeleine eventually lost contact with Jocelyn after she went on to marry Valentine.
Years later, Madeleine received a letter from Jocelyn, detailing the back-up plan she had created in the event that Valentine found her after she had run away: that she would put herself into a magically-induced coma with a special potion. Jocelyn knew she could still trust Madeleine to be someone who would never betray her to Valentine because of her unwavering hatred for him. Jocelyn also told Madeleine about Ragnor Fell so that, should she ever have to go through with her plan, Madeleine would be able to contact him someday, or pass on the message to anyone who could, when it was time to wake Jocelyn up. Madeleine never responded, but she had indeed read it and understood what she was being asked to do.
It was late 2007 when Madeleine came to New York, first meeting with those of the local Conclave; she was also among those who were dispatched to the Silent City to answer the Silent Brothers' distress call. When Malik Safar tried to stop Jace from escaping with Clary and Luke, Madeleine helped them by stopping him. She eventually made her way to the hospital where Jocelyn was being kept stable in her magical coma, where she immediately found Clary and informed her that she knew how to awaken her mother.
Not long after, the group of Nephilim of the New York Institute decided to go to Idris to look for Ragnor Fell with Madeleine. Before they could get through the Portal, however, they were attacked by Valentine's Forsaken warriors and Madeleine was killed in the encounter.
Madeleine had angular cheekbones with sharp features that Clary said didn't make her exactly pretty but made her striking in a way.
- Her last name 'Bellefleur' is a compound word that means Beautiful/Flower.