The Road Home (Marguerite Henry's Ponies of Chincoteague, Bk. 8)

Nina’s friend Leah has been acting oddly lately. The two of them attend the same small private school, and Leah also takes lessons at the barn where Nina keeps Breezy. But suddenly Leah seems to have lost interest in riding, and her behavior is oddly erratic. When Nina tries to find out what’s wrong, Leah pulls away.

At the same time, Nina becomes worried about Breezy, and discovers someone is sneaking in at night to ride him without permission! When Nina finds out it’s Leah whose family is having financial difficulties, she knows she has to do anything and everything to help her friend. After all, isn’t that what friends are for?