Garden of Madness by Tracy Higley
I liked the character of Tiamat. She is a strong female heroine who isn't very princess-like. She has a workout room where she punches bags and uses pulleys to strengthen her arms. She also races chariots, which is a unique sport in itself and even more unique when a princess does it. Tia is only satisfied with the truth and refuses to be used as a pawn by others. Other central characters, like Tiamat's mom and her late husband's brother, Pedaiah, are also fully developed and well-rounded.