Pennyroyal Academy (Pennyroyal Academy, #1)
by M.A. Larson 

2.5 out of 5 stars
A girl with no name arrives at the Pennyroyal Academy and signs up to be trained as a princess. She is given the name Cadet Eleven, which her new friends shorten to “Evie”. Gradually, Evie begins to realize that being a princess is not at all what she imagined, because the princesses are at war against the witches, just as the knights are at war against the dragons. They train to fight against the dark magic of the witches, using compassion and courage as their weapons.