Princess Megan and the Magical Tiara by Vivian French
Princess Megan is so excited about going to princess boarding school! Her grandmother gives her a diamond tiara before she leaves, and she can't wait to wear it at the Tiara Ball. When Megan arrives at Royal Palace Academy for the preparation of perfect princesses, she meets the terrible twins, Diamonde and Gruella. Will Diamonde get to wear Megan's special tiara to the ball instead?