Shadow, book 1: Wake of vultures
Lila Bowen2016

Nettie Lonesome dreams of a greater life than toiling as a slave in the sandy desert. But when a stranger attacks her, Nettie wins more than the fight.

Now she's got friends, a good horse, and a better gun. But if she can't kill the thing haunting her nightmares and stealing children across the prairie, she'll lose it all -- and never find out what happened to her real family.