Land of no angels

the long version

The Ascension marked a demon apocalypse that decimated the human race and forced survivors into hiding. Sixteen year old Rebecca Ashford and her younger sister, Errol, have spent the last year sequestered in their family's tornado bunker. When the sound of a screaming baby wakes them in the middle of the night, Errol attempts to save the infant and is poisoned by a demon. Now Rebecca must trust a mysterious tracker named Fox to take them to a secret survivor colony where they will learn how to save Errol's life. During the course of her quest, Rebecca gains the ability to use magic-specifically, the power to find lost or concealed items. Unless she can defeat frightening monsters and learn to use her power to locate the ingredients needed to cure her sister, Errol will die.