Edward Knight & Edward J. Knight 
Gunslinger [EPUB ebook] 
The Dragon of Yellowstone (A Gunslinger Beth novel in the Mythic West universe Book 1)

In an alternate Wild West where humans and monsters coexist, a teenage sharpshooter and her revolver must defend a fort from a deadly dragon. They say girls can't be gunslingers. Beth’s gonna prove ’em wrong. Even if she has to fight a dragon to do it. It won’t be easy to prove her worth while working as a hotel chambermaid in Golden City, Colorado. The famous battle that defeated the giants was fought thirteen years ago. The trolls remain confined east of the Mississippi. No one’s spotted a harpy since 1875. But Beth trained with the legends: the ghost of Calamity Jane gave her the gun, Wild Bill Hickok taught her to shoot. And at sixteen, she’s ready to make a name of her own. So, when strange assailants murder a visiting Arapaho shaman, Beth straps on her Colt .45. Without waiting for help, she must find the killers, defeat their dragon, and prevent the destruction of the West.