Cynthia makes her first appearance in book 4 of The Crush Saga.
Chaos - Book 4: http://www.amazon.com/Chaos-Book-4-Crush-Saga-ebook/dp/B00PL259B2/ref=sr_1_1?ie=UTF8&qid=1422360872&sr=8-1&keywords=4+peebles
Book Trailer for the series: http://youtu.be/4eMF8KXEUc4