Dark Moon Seasons (Four Horsemen of the Apocalypse Book 2) by Val Griswold-Ford

The Universe is Balanced. That tenet is taught to every Mage and Lord ever born. Light Magic, Earth Magic and Shadow Magic mingle on Earth, with portals to the Dawn Lands and the Shadow Lands dotted around it. Elemental Lords, spirits of magic, walk the Lands and interbreed with humans to produce Mages. The Council of Nine, made up of three Lords from each sphere, watches over the Balance and makes certain that no one tips the Balance in the wrong direction. If that happens, the StarChild will summon the Four Horsemen to Cleanse the world, and reset the Balance. Or at least, that s the way it has always worked before. Twenty-three years ago, a wealthy businessman started a series of illegal experiments with the assistance of two Elemental Lords. Combining cutting-edge technology and ancient magical spells, they took Light Magic and Shadow Magic and bound it into three unborn children. Unfortunately for them, the breeders carrying the children escaped into the night before the spells could be finished. Nikki Jeffries is a normal young woman searching for two things: the identity of her birth parents and the truth behind haunted houses. What she finds is another world entirely: a world of magic and mystery that she is swept into. Now, she must master her new-found powers and combat an ancient enemy of the Balance, or the Walls between the Worlds will crumble, and everything will fall to Madness.