Marietta Edgecombe

Marietta Edgecombe is a Ravenclaw student one year above Harry, with curly reddish-blonde hair, and is part of Cho Chang's cadre of giggling Ravenclaw girlfriends; her mother works for the Floo Network authority in the Ministry. Marietta joins Dumbledore's Army against her wishes out of peer pressure from Cho, and reluctantly attends the meetings. Later in the term, however, Marietta becomes an informant and betrays the group to Umbridge, which is not without consequences: the parchment that all the members signed back at The Hog's Head was jinxed by Hermione, which in turn caused purple pustules spelling the word "SNEAK" to break out across Marietta's face. Umbridge attempts to goad her into revealing crucial information, but Marietta is too terrified to show her face or even to speak. Kingsley Shacklebolt then swiftly and secretly modifies her memory with an Obliviate Charm. The "SNEAK" resisted all remedies to remove it, forcing Marietta into blatant and unsuccessful ploys to conceal it. Rowling revealed in a chat session after the release of Deathly Hallows that the "SNEAK" eventually faded, but still left a few scars.[6]
In the film adaptation of Order of the Phoenix, Marietta's betrayal is instead committed by Cho, under the influence of the Veritaserum potion. Marietta's name was seen alongside those of other D.A. members on the movie's promotional site and on some official merchandise,[7] but she did not appear in the film.