Her mother is sometimes seen as Ann Gunnell in various places but the records I looked at are without any documentation. If her mother's maiden name is recorded it might be found in Westmoreland County records.
Her father seems well-documented:
SAMUEL MOXLEY, born circa 1703, Westmoreland County, Va; died intestate, April 1768 in Fairfax County, Virginia, leaving two heirs, Samuel Moxley and Jemima Moxley. (Deed Book C-1, Page 827, Fairfax County). Samuel Moxley was deeded land in Cople Parish, Westmoreland County, by his father (3) William Moxley, Senior, on the 24th February 1721. (Deed & Will Book No. 7, Page 269 Westmoreland County.) The aforesaid land was later acquired by (4) Richard Moxley from Nicholas Minor. (Deed & Will Book No. 11, Page 454, 21 October 1752, Westmoreland County, Virginia.)
Edit: Mark, it appears there may be some questions about this lineage in WikiTree. May I suggest adding the tag Virginia to the question so that some Virginia Project people get a look at this.