According to family tradition, Evelyn M. Hill is descended from a long line of Texas horse thieves. (But when your family is not only Texan, but Irish, tall tales come with the territory.) This might explain why she devoted much of her childhood to writing stories about horses. Once she grew up, the stories naturally featured a tall, handsome cowboy as well.
She lives at the end of the Oregon Trail, where she gets to do all her historical research in person.