Your Louisa went by Nancy L. Brittain Carswell. I found her, I believe, in 1870. Her mother Elizabeth is listed as a widow. I saw several death records for Nancy L. and Zach Carswell. Louisa is always referred to as Nancy L. Twice she is mistakenly called Nancy Stacy. You need the 1860 Burke county census which I currently don't have access to. Good Luck.