Diabolique: A Sibyl Novella by Marlene Pardo Pellicer

This novella fills in a pocket of time for our heroine Ema, when she arrives in New Orleans in 1798, after battling dark beings in France during the last decade of the century as the streets ran red with blood from Madame Guillotine. However, otherworldly creatures are found in both the Old World and the New World, as well as treacherous humans. Who is an ally and who is an enemy, not everyone or everything is what they appear.