Mortal Follies by Alexis Hall

It is the year 1814, and life for a young lady of good breeding has many difficulties. There are balls to attend, fashions to follow, marriages to consider, and, of course, the tiny complication of existing in a world swarming with fairy spirits, interfering deities, and actual straight-up sorcerers.
Miss Maelys Mitchelmore finds her entry into high society hindered by an irritating curse. It begins innocuously enough with her dress slowly unmaking itself over the course of an evening at a high-profile ball, a scandal she narrowly manages to escape.
However, as the curse progresses to more fatal proportions, Miss Mitchelmore must seek out aid, even if that means mixing with undesirable company. And there are few less desirable than Lady Georgiana Landrake—a brooding, alluring young woman sardonically nicknamed “the Duke of Annadale”—who may or may not have murdered her own father and brothers to inherit their fortune. If one is to believe the gossip, she might be some kind of malign enchantress. Then again, a malign enchantress might be exactly what Miss Mitchelmore needs.
With the Duke’s help, Miss Mitchelmore delves into a world of angry gods and vindictive magic, keen to unmask the perpetrator of these otherworldly attacks. But Miss Mitchelmore’s reputation is not the only thing at risk in spending time with her new ally. For the reputed witch has her own secrets that may prove dangerous to Miss Mitchelmore’s heart—not to mention her life.