Amelia would have come from South Carolina is you look at William's land grant in 1763. Each person within the household was worth 50 acres, so with William getting 150 acres, one would assume that there was William, Amelia, and an unknown child in the household.
To date, no one knows her maiden name nor her descent. We do know she is NOT Native American because of multiple DNA tests agreeing with this.
On August 4, 1783, she is a witness to a Mecklenburg County, North Carolina deed from James Cochran to George Helms with her signature mark.
On February 13, 1798, she is named as wife of WIlliam Medcalf, Sr. in his will from Anson County, North Carolina.
On January 19, 1799, she gifts her dowery and what was left by the will of her husband, William Medcalf, Sr. to her son John Medcalf.