The Hope of Azure Springs by Rachel Fordham
Seven years ago, orphaned and alone, Em finally arrived at a new home in Iowa after riding the orphan train. But secrets from her past haunt her, and her new life in the Western wilderness is a rough one. When her guardian is shot and killed, Em, now nineteen, finally has the chance to search for her long-lost sister, but she won't be able to do it alone.
For Azure Springs Sheriff Caleb Reynolds, securing justice for the waifish and injured Em is just part of his job. He's determined to solve every case put before him in order to impress his parents and make a name for himself. Caleb expects to succeed. What he doesn't expect is the hold this strange young woman will have on his heart.