A friend of Cho Chang's who unwillingly joins Dumbledore's Army. Harry is suspicious of her from the beginning, and these suspicions later prove correct: Marietta outs Harry and the other students to Umbridge. This results in Marietta suffering from Hermione's cursed membership list, which makes acne-like boils spelling "SNEAK" appear on Marietta's face. She wears a balaclava on the Hogwarts Express home, suggesting that nobody is able to remedy the curse.
Marietta Character Timeline in Harry Potter and the Order of the Phoenix
The timeline below shows where the character Marietta appears in Harry Potter and the Order of the Phoenix. The colored dots and icons indicate which themes are associated with that appearance.
...It includes Neville, Dean, Lavender, Parvati and Padma, and Cho with one of her friends, Marietta. Luna, the entire Gryffindor Quidditch team, and several Hufflepuffs and Ravenclaws walk in as well.... (full context)
...everyone slowly improves. Cho blushes and makes mistakes when Harry is around. She explains that Marietta is so upset about being a part of the secret group because her mother works... (full context)
...then. Harry then hears Kingsley whisper and feels something brush against him. When Umbridge asks Marietta to tell them about the D.A. meetings, Marietta, whose eyes are strangely blank, says there... (full context)
...to curse Harry, but most of the D.A. comes to Harry's defense. Later, Cho and Marietta, who's wearing a balaclava, walk past the compartment, looking embarrassed. Hermione hesitantly says that Cho... (full context)