An interesting theory as to the identity of Barb'ry Ellen comes from Phillips Barry and Fanny Eckstorm the scholarly folksong collectors of Maine in the US who suggested that it was a libel on Barbara Villiers one of King Charles II's mistresses.
There is neither corroboration nor contradiction of this theory, but, certain pieces of evidence are interesting in suggesting that Scarlet Town the setting of some of the versions was colloquial slang for Reading in Berkshire, where Mrs Villiers received a large house from Charles.