The False Princess by Eilis O'Neal

Nalia is the crown princess and life is good, but just after she turns 16 she finds out her life is not what she thought.  She is brought to the thrown room and told that because of a prophecy foretelling the death of the princess before she was 16 that the real princess was switched with her as a baby.  Nalia is really Sinda, a commoner, filling in for 16 years to protect the real princess.  So she is shipped out to the only remaining real family she has which is an aunt in the woods far away.  Sinda, obviously, has a hard time adjusting from doing needlepoint and studying different languages to cooking and cleaning, but she does discover she has magic.  This discovery leads her back to the palace where she discovers a much darker plot that will destroy the kingdom which sends her on a journey to save it and find her true self.  A really great read.  Sinda seems rather weak at first, but she finds her strength and who she is in the end.  A fun read with a little romance, magic, deception, and adventure.  An impressive first novel for Eilis O'Neal.