"She's a lovely person really. She just made a mistake..." --Cho Chang (OP28)
A friend of Cho Chang’s with curly, reddish-blonde hair, Marietta was dragged to D.A. meetings by Cho and signed her name to the parchment that listed members of the group (OP16). However, when she later betrayed the group to Umbridge, she discovered the parchment had been jinxed, and her face broke out in nasty pimples spelling the word “SNEAK” (OP27). When Umbridge attempted to extract further information, Marietta refused to say anything else incriminating, and then had her memory modified by Kingsley Shacklebolt (OP27). Even months later, the pimples were still visible (HBP7). Eventually, the pimples faded, but left scars (BLC).
"Marietta" = little bitter