Sadie Chapman 
My Personal Fables [EPUB ebook] 
(Book 1: the Legend of the Horse)

The story begins with Pegasus choosing three of his best pairs of beautiful white winged horses from Olympus to come to Earth for a special purpose to become a new species that not even the Greek gods had seen or known before.
They become The Earth unicorns, The Day unicorns and the Night unicorns and with their magic they will heal and protect the earth after the dinosaurs reign.
The story then follows on about a special mare and her life that will change completely forever, has she has been chosen to be something even greater than a magnificent; magical Unicorn that she already is!
And through this great change she will create her own miracles along the way!