Linda Chapman 
My Secret Unicorn: A Winter Wish [EPUB ebook] 

It all started when Lauren first moved to the countryside from the city and discovered that her ordinary little pony was anything but ordinary, for when she recited a secret spell, Twilight turned into a unicorn with magical powers! From that moment on, Lauren and Twilight learned how to use magic to help their friends solve their problems. And now Lauren and Twilight are back in a magical new and exciting wintertime adventure.