The Key to Her Chest by Misty Malone

Naomi Henderson has been working with her grandfather, Will, who is a doctor. He and his wife have raised her since her father's death, in a small town in Wyoming in the late 1800s. He's passed his knowledge on to her, and the town trusts her and considers her to be their second doctor.

Will's brother, Jeb, comes to visit, and it soon becomes clear to Naomi and the town of Cedarville that he's nothing like their beloved Will. When Will dies tragically, Jeb comes to town again and causes one problem after another, while the town rallies around Naomi. A local sheriff tries to sort out one such problem, but soon finds himself trying to sort out the feelings he's developing for the little fireball of a doctor.