You'll find a lot of info about Withers (and a lot of other families) on this web site under "Court Records" http://www.historiccourtrecords.org/ i.e, there's a court record concerning George L. Ball & c to James Withers & co Fauquier Co. - 1823. Mentions Aggy Withers mar. to Martin Porter; Aggy sister to Lewis Withers.