Island of Exiles by Erica Cameron - Chapter 1 to 11

In Khya's world, every breath is a battle.

On the isolated desert island of Shiara, dying young is inevitable. The clan comes before self, and protecting her home means Khya is a warrior above all else.

But when following the clan and obeying their leaders could cost her brother his life, Khya's home becomes a deadly trap. The only person who can help is Tessen, her lifelong rival and the boy who challenges her at every turn. The council she hoped to join has betrayed her, and their secrets, hundreds of years deep, reach around a world she's never seen.

To save her brother's life and her island home, her only choice is to trust Tessen, turn against her clan, and go on the run-a betrayal and a death sentence.