I found out! The author did an interview with Entertainment Weekly which also features the cover for the new book, Misguided Angel, which will be released on October 5, 2010. If you have read these books and find them intriguing as I do, then you will love this article.
Melissa De La Cruz Interview
My own opinion, this is my favorite cover of them all. The most beautifully crafted anyway. And she is one author that I want to walk up to and say, "Where did these ideas come from?"