Claire De Lune by Christine Johnson
From Goodreads: Torn between two destinies? Claire is having the perfect sixteenth birthday. Her pool party is a big success, and gorgeous Matthew keeps chatting and flirting with her as if she's the only girl there. But that night, she discovers something that takes away all sense of normalcy: she's a werewolf. As Claire is initiated into the pack of female werewolves, she must deal not only with her changing identity, but also with a rogue werewolf who is putting everyone she knows in danger. Claire's new life threatens her blossoming romance with Matthew, whose father is leading the werewolf hunt. Now burdened with a dark secret and pushing the boundaries of forbidden love, Claire is struggling to feel comfortable in either skin. With her lupine loyalty at odds with her human heart, she will make a choice that will change her forever?
This sounds sooo good! It's published in the UK by Simon and Schuster 5 Aug 2010 and is published in the US May 18th 2010 by Simon Pulse