A Cowboy's Angel (Harlequin American Romance Series #1496)

Uneasy Allies 

Mariah Stewart has a passion—to save racehorses from slaughter once they're done racing. Zach Johnson has a passion, too—raising winners. Mariah and her protests are one more annoyance on a list that may cost him his family stables. And when his best horse goes down, she pesters him about his plans for it. The thing is, Mariah is also a vet. Her crazy proposal to save Dasher might work, and what does Zach have to lose? 

Only his sanity! Maybe his determined bachelorhood, too. Because Mariah just…gets under his skin. Zach knows she feels it—she heats up every time he's near. But is the attraction between them enough to set aside everything they believe in?