Book 2 Princess Ellie's Secret by Diana Kimpton

It's been years since Ellie learned to ride on Shadow, her little Shetland pony. Now her feet touch the ground when she's riding him When the king sees how redicilous she looks, he orders Shadow to be sold. But Ellie can't bear to lose him. She got to think of a secret plan to save Shadow, and time is runing out!