The Sandcastle Empire / Kayla Olson.

When the world is taken over by a brutal ruling body that controls the planet's resources, Eden resolves to survive by finding her way to a neutral island where her efforts to track down a friend are challenged by enemies and traps. Before the war, Eden's life was easy. Then the revolution happened, and everything changed. Now a powerful group called the Wolfpack controls the earth and its resources. And even though Eden has lost everything to them, she refuses to die by their hands. She knows the coordinates to the only neutral ground left in the world, a place called Sanctuary Island, and she is desperate to escape to its shores. Eden finally reaches the island and meets others resistant to the Wolves. But the solace is short-lived when one of Eden's new friends goes missing. Braving the jungle in search of their lost ally, they quickly discover Sanctuary is filled with lethal traps and an enemy they never expected. This island might be deadlier than the world Eden left behind, but surviving it is the only thing that stands between her and freedom.