This card is of Laura Locoul Gore (1861-1963). Photo taken in 1886 (so she was 25, or almost 25). "Laura, last lady president of the sugar plantation, is dressed as Mephistopheles for Mardi Gras in New Orleans." (back of the postcard). "Mephistopheles (also Mephistophilus, Mephistophilis, Mephostopheles, Mephisto and variants) is a name often given to one representation of the devil or Satan. It is also the name used for the demon in the Faust legend." Wikipedia.
Interesting - I guess that explains the pitchfork! Thanks Meaghan!