Fairy Blossoms #2: Poppy and the Vanishing Fairy by Suzanne Williams

Mistress Lily is gone for the day, and Poppy hopes she'll hurry home. Then Mistress Lily doesn't come back on time—something must be wrong! With the help of their flying ponies, Poppy and her friends set off to find out what's happened to their teacher. They discover a magical creature and a mysterious enchantment!