Summer Horse — Barbara Morgenroth

Two girls plus two horses equal  a summer of calamity and escapades.
Nicki and Wynne share a love of horses but not of adventure. Nicki finds
herself being dragged by the strong-willed Wynne on trail-rides through
thunderstorms, pig chases, hunts and a horse show with an escaped pony
trying to find her stablemate, even if he's busy jumping on the outside course.
Fearless and glued to her saddle, Wynne wants to turn Nicki into a real rider.
Can Nicki survive Wynne's plans for her? By the end of the summer, will Nicki have a horse of her own?

Middle Grade--readers 9-12 years of age