The Scorpion Rules, her most recent book, fits this description to a t.
In a future world, desperate for peace, a collective bargain was made. An artificial intelligence known as Talis keeps watch over the various nations of Earth, enforcing peace with the threat of death. Cities are destroyed when the peace is broken. And hostage children, the dearest ones of the various rulers, are gathered together in an enclave, knowing that they will be killed if their nations go to war.
One of these so-called Children of Peace is Greta, daughter of a queen of North America. If she can make it to 18 years old, she will be free, and so she calmly goes about her life, being instructed by her AI teacher, working on the enclaves farm, keeping to the pattern of the days dictated to her. She is so much the good hostage child that she doesn't even sneak off with the other teens to play "coyotes" (euphemism!) in the dark night outside. But then a catalyst from outside shatters the calm of her life. Elian, son of a new American alliance that is threatening to make war with Greta's homeland, arrives, and he refuses to be a docile hostage. He is tortured as a result, while the other Children of Peace watch. And Greta knows that his people declare war on hers, which seems likely, the two of them will die.
Her peace of mind is cracked both by the horrible implications of his presence, and by his stubborn defiance. And a new Greta emerges from the structure of her controlled life, one who questions, who loves, who wants a future of her own making....But Talis is watching, always watching, and for him, death is not just an abstract threat.
So basically the book is about Greta growing from Good Hostage Child to strong, passionate, questioning young woman, and as this happens, there's a very gripping ratcheting up of the tension not just of her personal situation but of the lives of those around her, and the lives of thousands of strangers who Talis could kill at any time. I was so afraid reading it that it would have a heartbreaking ending, and was glad that although tense as all get out, it wasn't all devastation and darkness....There is lots and lots of room for a sequel, but it ends at a good ending point, where there is hope (hanging fro a thread) for a different sort of peace to come.
I don't want to spoil things, but I do want to say, to help those who want to find such books, that the teen romance at the heart of the book is LGBT, and this was an unexpected and tender romance that tightened the knot around my heart just beautifully!
In short, The Scorpion Rules isn't exactly a comfy kids at a farm school fooling around with each other sort of book, although almost it is (I put my boarding school label on it!); instead, it's that sort of book but with the very real threat of death, and no possibility of escape, hanging constantly over the kids, beautifully written and achingly engrossing. I read it two months ago, and it is still crystal clear in my mind.