I Committed a One-Night Mistake with the Young Lady?

Listen to me... When I woke up, my lovely young lady had turned into a handsome duke...!! The novel, "The Saint Punishes Evil," is the story of Saintess Lune defeating the villainous Duke Clovis. Our protagonist is reincarnated into this novel's world as Leila, a fresh-faced apothecary hired by the ducal family where Clovis lives! To be hired by the villain's family of all places! Shaking with fear, Leila goes to greet Clovis, but finds a beautiful, pitiful-looking young lady instead...!? This isn't the novel world I know, is it? Leila feels a little relieved, but after learning about the young lady's unfortunate circumstances, she works hard to make her happy!! She has no idea that this young lady is actually the villainous Duke Clovis, cross-dressing for certain reasons...