This book reminds me (in a good way) of the classic Faro’s Daughter by Georgette Heyer.
From the book blurb:
Daphne Ingleside’s visit to her Aunt Effie in London was meant to add a little spark to her placid country life. And it did—once the two women decided to write Effie’s memoirs. For Effie, a faded divorcée, had been the beauty of London in her day, and many of the ton feared their misbehavior would be disclosed. The Duke of St. Felix, misinterpreting their project as a means of blackmailing his family, antagonized the sharp-witted, beautiful Daphne to his peril.