Twilight magic
The author is Linda Chapman and it is illustrated by Ann Kronheimer.
The characters are: Twilight, Jade, Lauren and her friends.
The story is about a girl named Lauren who had a unicorn and his name was Twilight. The mare at the stables had a foal and Jade was really jealous that Lauren made new friends with the foal. Twilight was magical because when Lauren said the magic words Twilight transformed into a unicorn. One day Lauren and Jade were in a competition with their ponies and Jade got hurt. Lauren and Twilight helped Jade and finally they made friends.
I recommend this book because it has a very interesting story.