I have a fair amount of info on the Pamplins in Amherst Co., VA in the late 1700's and early/mid. 1800's. But I don't find record of a Mary Pamplin marrying a Smith.
I have a Wm. Pamplin who md. in Amherst Co. on 18 Feb., 1793 to Mary Wright. Their 8th child was Mary Jane Pamplin. All I have on her is that she married a Mr. Gordon. Perhaps Mr. G. died young and she supsequently married Smith.