The Reign of the Occult by Lauren Louise Hazel
The battle between the Underworld, full of darkness, and the Overworld, full of light, has been evenly balanced for millennia. Caught between them is the mortal world, where humans have become so afraid of a magic they cannot understand or control that they allow the Occult to rule them. After the Occult joins forces with the Underworld, the balance shifts and the Overworld is decimated.
But still, in the mortal world, the magic won’t die. It appears when a supernatural being and a human have a child, like Prue.
This is the first volume in an epic new fantasy series that spans the three richly detailed worlds as Prue, her non-magical half-brother Everett, and all Magic Users, fight to survive. They are being hunted by the Occult, who turn the Magic Users they capture into tools to eliminate their own kind and, eventually, to destroy all traces of magic.