Nyima Rewa never wanted to be a fighter. Her greatest aspiration was to control her vis, a sense that allows her to perceive and manipulate most forms of energy. Like all people who can use their vis, called Children, Nyima took an Oath to always use her abilities for the
betterment of her country. Under normal circumstances that would have been a peaceful enterprise, but Nyima's country, Bod, was invaded. For years she upheld her duty and defended her people, until Bod was conquered. Now her people work to keep their culture alive in exile.
It isn't home, but it's peaceful.
At least until Nyima gets a letter from an old friend, Odhràn Torley. Odhràn's country, Eikrengt, isn't at war, at least not yet. But the way Odhràn's old enemy is stirring up trouble, civil war might be just around the corner. (your hook starts here --->) The last thing Nyima wants to do is get involved in another war, but stopping a war before it starts - that would be worthwhile. And after Odhràn risked his life to help her people all those years ago, she can't refuse. So she agrees to lend Odhràn and his followers her expertise in espionage and hidden war.
But to help him, Nyima might have to kill - something she swore never to do, even to save her friends or herself. No matter how many of her oaths she's broken, no one has a right to ask her this. Do they?
Lose the backstory, focus on her dilemma.