My Secret Unicorn: Flying High and Starlight Surprise By Linda Chapman

Most of the time, Twilight looks like an ordinary grey pony but when Lauren says the words of a spell he transforms into a magical unicorn and together they can fly all over the world . . .
Lauren's friend Jessica is finding life at home difficult, so difficult that one day, two weeks before her dad's wedding, she runs away. Lauren and Twilight want to help her but their magical plan means letting Jessica into their secret life. Can they persuade her to trust them so they can help her feel like she's flying high again?