Mary Arthur McElroy
Mary Arthur McElroy was the sister of the 21st President of the United States, Chester A. Arthur, and served as a hostess for his administration . She assumed the role because Arthurs wife, Ellen Lewis Herndon Arthur, had died two years earlier.
Mary Arthur was born in Greenwich, New York to William and Malvina S. Arthur. She was the last of nine children. She attended the Emma Willard School Seminary in Troy, New York and later married insurance salesman John McElroy. They lived in Albany, New York and had four children.
Source: Wikipedia