My Secret Unicorn: Dreams Come True (My Secret Unicorn #2) by Linda Chapman

'Shadow, please!
   You've got to jump!'

Lauren's pony, Twilight, turns into a beautiful unicorn when she says the magic words.

When Shadow, a young pony, is too afraid to jump, only Twilight and his magic can give him the courage to overcome his fears. Then one stormy night. Shadow has to face danger alone . . .

Read more about Lauren and Twilight's magical adventures in My Secret Unicorn: Flying High