Hear my words and heed my warning and laugh if you dare: witches live among us!
-- Mary Lou Barebone (WFT)
Mary Lou Barebone was the fanatical leader of the New Salem Philanthropic Society, an anti-magic group active in New York during the 1920s. A “handsome” woman who wore Puritanical clothing like her Scourer ancestors, Mary Lou was also mother to three adopted children whom she raised inside the New Salem Church building: daughters Chastity and Modesty, and a son Creedence (WFT). Mary Lou’s abuses as a mother led directly to her death when she was attacked by an Obscurus while trying to punish her children with a leather belt for having a toy magic wand. She was flung into the air and the church destroyed around her. Her body with strange markings on the face was found in the ruins by Auror Percival Graves, who sought to find the Obscurial responsible for her demise.
Mary Lou was a descendant of evil Scourers who caused the Salem Witch Trials through her ancestor Bartholomew Barebone. He carried on the family tradition when he tricked Dorcus Twelvetrees into telling him all about MACUSA and Ilvermorny School in the late 1700s, an act which led to Rappaport's Law, keeping No-Majs and Wizards entirely separate.
A "charismatic and earnest" leader of her anti-magic cult
"Barebone" hints at the Puritan Sourer legacy Bartholomew Barebone and his family carry on; first, it alludes to the austerity of Puritan sensibilities; second, Praise-God Barebone was an English Puritan of the Commonwealth/Interregnum (the period of English history between the English Civil War and the Restoration of the monarchy, when Puritans basically controlled the government and instituted reforms related to their religious and moral beliefs) who belonged to a sect particularly concerned with Judgement Day and whose name is used in reference to the appointed parliament which immediately preceded Oliver Cromwell being made Lord Protector (Barebone's parliament). (Sources: Wikipedia 1, 2, 3, 4, 5)
From the Web
Mary Lou Barebone on Harry Potter Wiki