I am just running across this post here because I am also trying to dig around on the Dungy side of my family. My 3rd great grandmother's name was Mary Ann Dungy (b. July 1840) and she married a George Mayo of Cumberland County.
It is funny that you stated about this Mary Ann Brown, because when we went to Cumberland researching records, if my memory serves me correctly, this was one of the last names we saw for her mother (either Marjy or Nancy Brown (Dungy).
Have you found any more recent information on this family line? Please email me: firstname.lastname@example.org