Vampire Affliction: The Vampires of Athens, Book Two

Gertie has become friends, and has possibly fallen in love, with both a demigod and a vampire, who happen to be at war. Although she sympathizes with the vampire uprising and has even become a vampire herself, she distrusts the leaders, especially when they plan to kill humans to cull out the demigods before ambushing them. As the three unlikely friends discover that neither side is perfectly good or evil or right or wrong, they work together to try to bring about the best outcome; but, when their parents and the gods undermine their efforts and hang them out to dry, the three teens realize they're on their own and no one will save them.