Here Comes My Earl by Anna Bradley

Euphemia Templeton can’t wait to put the London season behind her forever, but before she can retire to the country in blessed obscurity, she has one final promise to keep. She must find a proper match for Lady Harriett Fairmont, who is embarking on her second season.
Matchmaking is easy for a lady with Phee’s skills, but when Harriett’s elder brother James, the arrogant, infuriating, and far too handsome Earl of Fairmont accompanies his sister to London, she soon has cause to regret her promise.
James doesn’t believe in matchmaking, he doesn’t approve of Harriett’s favored swain, and most of all, he doesn’t trust Euphemia Templeton, no matter how clever she is, or how charmingly her lips purse when he argues with her.
James and Phee challenge each other at every turn, but when a battle of wills becomes a battle for hearts, will Phee discover the only lady in London she can’t successfully match is…herself?