The Wallflower Dares the Duke by Alyssa Clarke

Miss Honor Shelton never expected to find herself at the center of a scandal. When a notorious rake attempted to steal a kiss because of a reckless bet, Honor did what any respectable lady would—she punched him and sent him sprawling. Unfortunately, they were discovered at the worst possible moment, and the situation was misinterpreted as a passionate tryst. Now, rumors are swirling, and her beloved sister’s debut season hangs in the balance.
With no suitors willing to risk their reputations, Honor faces ruin. But then the Duke of Windermere, one of the most eligible men in society, offers a surprising solution: a fake courtship. If society believes a duke is paying Honor attention, the scandal may be undone.
As their staged romance progresses, the last thing Honor expects is to fall for the enigmatic and elusive duke—but resisting him may prove impossible.