Although there may be a connection somewhere, I don't think the Mary Stephens who married William Kerby in 1877 is the same as the Mary Stephens listed in the 1860 Dekalb Co, TN census. The Greene Co marriage license shows William's bride to be 21 years old in February of 1877. This indicates she would have been born about 1857. The Mary Stephens listed in the 1860 Dekalb census was born about 1837. Your Mary Stephens is about 20 years older than my gggrandmother Mary Stephens. Also, though the census information is often inaccurate, my gggrandmother's birthplace is listed as AR in the census records I have found.
I can email you more information if you like - just let me know if you are interested.