>> Ive also read that she very closely resembled his deceased wife <<
Wasn’t her mother a 1/2-sister to TJ’s white wife? If so, Sally was the wife’s niece.
(And Sally was a quadroon — or as some said of her, “Dern near white.”)
Sally Hemings was Martha Jefferson’s half sister. John Wayles was the father of both Martha Jefferson and Sally Hemings