Elizabeth Bear

Every cowboy story needs a horse no man can ride. No man-but Miss Karen Memery is all woman. When she and her beloved Priya sign on to do stunts for a motion picture about a rogue Mechanical named Cowboy and a Wild West show, she finds the horse of her dreams: Angel Maker. Her plans to rescue him from a deadly stunt are ambitious enough, but she's soon beset by even greater threats when two men are murdered brutally.
Cowboy and Priya are arrested for the crime, and Karen must prove them innocent-and save the life of the wild stallion too!