Well, "Nancy" certainly began as a nickname for "Anna" and was so used in this time period. Anna (Ford) Jenkins may well have been called, "Nancy". I don't have any evidence, one way or the other, though.
I wasn't suggesting that Anna (Ford) Jenkins and Nancy (Cavendish) Hannah were the same woman. I was suggesting that Nancy (Cavendish) Hannah, at least from what I've seen so far, is likely the Nancy mentioned by Wm Hunter Cavendish in his will.
I haven't pursued the question in Lewisburg and Warm Springs, but after spending far too much time searching on-line, I don't see convincing evidence that Anna Ford was a daughter of Cavendish. I've seen a published history, written in 1916, that says "Hunter Cavendish", in the name of Wm H C Jenkins, "perpetuated the family names...of his mother". The father is stated to be Azariah but the mother is not named, something that may suggest the limits of the author's knowledge or even the family's knowledge by that late date.
The fact that Cavendish was surety on the marriage bond in Greenbrier doesn't necessarily suggest that he was a blood relative of the bride and, even if he was a blood relative, he wouldn't have to be her father. Assuming the quote above is true, it could also imply that Wm was Anna's brother or even a maternal uncle.