Flora, Lily of the West is a British Isles song, probably of broadside origin. The usual tune was earlier used for the song Caroline of Edinburgh Town, and would appear to be Scottish. Some of those broadsides credit it to a G[eorge] Brown, also sometimes credited with The Constant Farmer's Son and The [Bonny] Bunch of Roses. These are generally supposed to be Irish (the tune to which the latter was specifically set certainly is) but commentators have occasionally been puzzled by the fact that "George Brown" isn't a particularly Irish name. There's no particular historical need for him to have been Irish, as it happens. Napoleon was just as appealing as an iconic figure to English radicals as he was to Irish nationalists; and for the same reasons, though this is often ignored by people who don't look beyond "received wisdom" on the subject.

There are plenty of songs which became popular in Britain and Ireland from the 19th century onward which had their beginnings in America. These often went unrecorded by the folk song collectors of the early 20th century because they knew them to be popular commercial songs of relatively recent composition, and that wasn't what they were looking for; as often as not, they knew them already.