It's My Ranch by Misty Malone

Jake Hamilton thought he had his hands full when he inherited his grandfather's ranch at a young age. But he was shocked two years later when he was told he was to inherit his neighbor's ranch, as well, with one proviso. He was to watch after his neighbor's 19-year-old daughter, keeping her safe and providing a place for her to live until she married.

Jake didn't know Loretta that well, but her lack of safety bothered him immensely. The first time he met her she was on his land, doing something so dangerous he instinctively pulled her off her horse and across his knee for a spanking. Neither of them were happy to hear the conditions of her father's will, but out of respect for him, Jake was determined to do as her father wished.

She fought him every step of the way, until after ignoring his safety rule yet again she finds herself in serious trouble. Now she has to hope he cares enough to go looking for her and can find her in time.