According to Dunavant, 1947:81:
Major John Cowan married Mary Walker, his cousin, 1768. He was killed by the Indians on the Clinch River, 1778-1780. Mary Cowan was captured at the same time, with her small daughter who was later killed, and her son James, 15 years of age. He was captured by the Cherokees and escaped after one year. His mother, Mary Cowan was taken north by the Shawnees, and escaped after seven years. 
Many Cowan researchers rely on Source:Fleming, 1971 for information on the killing of Major John Cowan, and the captivity of his wife, Mary Walker. Fleming derived much of his information from Mrs. Dunavant. For a discussion of Mrs Dunavants work go here.
Mrs Dunavant derived much of her information from the letters of JB Cowan, transcriptions of which she included in her discussion. Fleming apparently used her work as his source for the versions of the JB Cowan letters that he included in "The Cowans of County Down". In any case, both Fleming's and Mrs. Dunvant's version of the story of the Killing of Major John Cowan are ultimately based on JB Cowan's letters. While there are differences between Flemings presentation (which is the one known to most Cowan researchers), and Mrs. Dunavants presentation (known to few), neither Fleming nor Mrs. Dunavant add anything substantively new to the story. (Mrs. Dunavant did provide information about events in southwest Virginia, based on recollections contained in the Draper MSC. These additional information sources, however, added nothing to the basic story about Major John and wife Mary.) Thus, when we evaluate the story itself, it is JB Cowan's presentation that we need to be concerned with, not with the version described in Dunavant, 1947, much less that described in Fleming, 1971
Mrs. Dunvant cites several sources for her information with regard to the family of Major John Cowan:
Tracking down Mrs. Dunavant!
Another work by Mrs. Dunavant is Robeson County Census of 1850 Mrs. H J Dunavant (DAR). This would seem to be a census extract, and unrelated to present concerns.