I've just noticed that Furry Lewis gives the name of John Henry's wife as "Nella Lee."
I don't know which of the several times Furry recorded "John Henry" this is, but it is obviously a concert recording, so it must be from his rediscovery period.
In any event, this gives a little reinforcement (some might say "very little") to Neal Pattman's version, naming John Henry's wife as "Maggadee," which sounds like "Maggie D" and may be a reference to Margaret Dabney, the wife of the Henry Dabney who appears in the Copiah County census of 1870 (and 1880 as Henry "Dabner") and who may be both the "Henry" who was Captain Dabney's father's slave and the "John Henry" of legend.
Names commonly found are "Polly Ann" and variations, but "Mary Magdalene" occurs rarely (including Lead Belly's version), "Maggadee" once, and "Nella Lee" once (to my knowledge). These last three are rhymes or near rhymes. As I have noted previously, "Maggadee" is a logical precursor of "Mary Magdalene" because "Maggadee" sounds like "Magdalene" and to many people you can't have "Magdalene" without "Mary." "Mary Magdalene" would degenerate to "Mary Ann" for a couple of reasons ("Magdalene" is too big a word; "Ann" provides a near rhyme for "sand") and "Polly" is a common nickname for "Mary." "Polly Ann" is an attractive commonplace and represents a stable end point of these name mutations.
"Nella Lee" could be another mutation of "Maggie D"/"Maggadee." They rhyme and they have the same number of syllables. "Maggadee"'s lack of familiarity and awkwardness would provide the impetus for change. "Nella Lee" sounds a lot more like a plausible name.