Tomris Laffly Herding cattle is a woman’s work in Emelie Mahvadian’s meditative “Bitterbrush,” a picturesque documentary that embraces the sweeping tradition of the Western genre. The brawny job comes naturally to the nomadic Hollyn Patterson and Colie Moline, two close friends who are seasonal range riders for hire in the remote American West, cowgirling their way from one temporary job to the next, deep through the mountains and prairies of the Idaho terrain.