The Irish influence in Louisiana (and the music thereof) can be found at the River of Sound website here:

http://www.pbs.org/riverofsong/music/e4-new.html

To understand why it is seriously plausible that the song was originally written by an Irish American, see this website with a pictorial history of the New Basin Canal, built to connect New Orleans to Lake Pontchartrain in the early 1830s by Irish immigrants, who settled in the area.

http://schools.bigchalk.com/members/lakeshorelinks/subpage/newbasincanal

FWIW, I'm a Mississippi River folkie who first heard the song titled as "My Creole Girl".