The Kin Chronicles

A portal teleports Shelby Pardow to the planet Azimuth, where she is not a child but a warrior, Kin to one of the six Aulic Assembly members imprisoned by Malefic Cacoethes, the evil spawn of the demon Biskara. He razes towns and cities in his quest to rule Azimuth, and yearns to turn his forces against Earth. Shelby must learn to kill and lead an army into battle, or Azimuth—and Earth—will fall.