The King's Feather - Under His Wings, #1

Pero Moshe's mom vanished from their Oregon home, and the prophecy says it will happen to Pero, too. But when it does-and Pero is transported to an older universe, life gets more than a little nuts. Throw in a bodyguard who is almost criminally cute, a corrupt and brilliant doctor who wants to steal Pero's power and rule all of Moon City, and her mom showing up as a pawn in the whole thing. And all Pero wants is to grab her mom and go home.
But, uh, yeah, that's not happening. In the end, Pero is forced to choose between forgiveness or escaping with those she loves before a shout crumbles Moon City's walls to pieces. And both choices come at a cost she's not sure she's willing to pay.