Moonsilver — Kathleen Duey

Heart Trilby has no family. She lives a hard and lonely life in the dusty village of Ash Grove -- until she finds a scarred, skinny mare in the forest. Against the wishes of her guardian, mean-spirited Simon Pratt, Heart adopts the mare and names her Avamir. Heart is thrilled when she realizes Avamir is in foal. But when the colt is born weak and disfigured, Simon decides to sell Heart's beloved horses to be slaughtered by the town's soapmaker. Can Heart find a way to protect them -- and the only love she has ever known?