There's a student named Mary Cheatham in the rolls of the Mordecai school. She was there for one year, 1814 (both sessions), and a William Cheatham is the name associated with her account. William Cheatham appears in the Mordecai ledger, paying for "Miss Mary," in April 1814. (William Cheatham also appears on the page for February 1816, without a child's name attached, possibly meaning he lived near enough to Warrenton or to the Mordecais in other places to have further dealings with them; or perhaps he had a niece who attended after Mary's time there.)
I'm guessing that Mary Cheatham might have been from Chesterfield County, Virginia, only because a lot of Cheathams lived there. But I can't find a William with a daughter Mary the right age. Their names are too ordinary; and Mary might have gone by Molly or Polly or May later in life, and the Cheatham might have been spelled Chatham in some records. The usual story!
Next entry: another boy's name in the school rolls.