A Touch of Magic by Linda Chapman

Lauren's pony, Twilight, turns into a beautiful unicorn when she says the magic words. turns out to be as special and as magical as Twilight, but her little brother Max disagrees. He has grown tired of looking after Buddy, his big, lively puppy and leaves him all alone while he goes out to play on his skateboard. But one day Buddy goes missing and Max is distraught. Lauren secretly turns Twilight into a unicorn and together they fly over the woods in search of the young dog. They find him, but he's badly injured. Twilight uses his new-found healing power to save Buddy. Max promises never to neglect his pet again - after all, you can't be best friends with a skateboard like you can with a dog!

This book is part of the "My Secret Unicorn" series.
Here are some other books from this series: