The parents of Susan Kirby have not been determined. It is known that they were born in South Carolina, as was Susan. There are over 20 Kirby heads-of-household on the 1840 census for South Carolina. Of those, five (William, Tery, John, Green and Hawkins) are from Spartanburg County where Susan and Alexander LACKEY married. All of these seem to be too young to be Susan's father.
After Susan married Alexander LACKEY, they lived for a time in South Carolina before returning to Alexander's home in North Carolina. It is possible that they were living with Susan's parents.