You ask how I can prove Nancie Sheffield is the daughter of Seaborn Sheffield. The 1880 Census shows Seaborn Sheffield living in Damascus, GA as a 54 year old (birth year 1824) single man, working as a farmer, with his 2 daughters Eller, age 12, and Nancie, age 14. Both girls are listed as being "at school." Moreover, the newspaper accounts of his death mention his daughters and the fact that he legitimated them. I also have a partial transcript of Seaborn Sheffield's murder trial, which also mentions his daughter Nancy.
If anyone has any information about Nancie (Nancy) Sheffield's mother, please let me know.