The Trial Region (Fantasy Dystopian Novel?)

In a place called the Trial Region, an evil overlord has come to power...the Overseer. The Trial Region is split up into 5 districts, the Pyrozone, the Cryosphere, the Electrosector, the Hydroward and the Grid. There used to be another called to Terradomain, before the Overseer destroyed it 1000 years prior. The Overseer resides in the Grid, attacking and attempting to take over all the other districts. But was the Terradomain *actually* destroyed? No. a small island lived on, now only going by Terra. Nobody except the surviving Terra residents know it still exists, and they all keep a low and cautious profile. When the island of Terra is accidentally spotted, their new ruler, Rio, goes on a journey to destroy the Overseer once and for all, before he gets to the rest of the Region. A series of challenges awaits her as she attempts to fulfil this seemingly impossible task. But with the few friends she makes along the way, how long can 'impossible' really hold someone off??? (more info inside)