Brenna Strachan Series by Hadena James

Brenna Strachan is half-Demon, half-Witch and its the eve of her 30th birthday. This means that she will stop aging and come into all her Demon powers. But there are forces at work hoping to keep her from Maturing. They must kill her in the short time that she is mortal. If they fail, she will take her place among the most powerful beings on Earth. While Brenna struggles to stay alive, she must also struggle to find out exactly who she is and come out of her parents' shadows.