Ashes trilogy (Ilsa J. Bick)

Alex, a resourceful seventeen-year-old running from her incurable brain tumor, Tom, who has left the war in Afghanistan, and Ellie, an angry eight-year-old, join forces after an electromagnetic pulse sweeps through the sky and kills most of the world's population, turning some of those who remain into zombies and giving the others superhuman senses.

"Alex and Tom's future is uncertain as they continue the struggle to survive in a post-apocalyptic world, and their lives are threatened by the Changed and other human survivors"