The Secret Queen — Mark Miller

In this third book of the Empyrical Tales, it is a year after the events of The Lost Queen. Zandria and her younger sister, Olena, seem to be growing apart. But now, Olena has mysteriously disappeared without explanation. To make things worse for Olena, she is having trouble with her magical abilities. With the help of an unusual bronze ring, Olena leaves the crystal Castle Empyrean in disguise. She soon steps into a land of giant crocodiles, unending deserts, ancient pyramids and even mummies! Now Olena must discover the truth about the dinosaur-like race that lives beyond the southern border before they attack Empyrean. All the while, she struggles with faith in her own abilities. Will Olena regain her magic in time? To find out, she has to become The Secret Queen.