In the 1910 Victor Herbert/Rida Johnson Young operetta Naughty Marietta (the source of "Ah! Sweet Mystery of Life!"), the heroine, Marietta, escapes an arranged marriage in Italy by sailing to New Orleans as a casquette girl in 1780. The New Orleans of the opera is still under French control even though by that year in RL, it was owned by Spain.
Now I'm planning another fantasy novel based loosely on NM, only the New Orleans analogue is called New Bordeaux, situated on a Louisiana island called Saint Domingue (from the colonial name for Haiti), and Marietta is a courtesan.
What's a POD that would keep Louisiana as a French colony in 1780?