Sisters of Misery by Megan Kelley Hall

There are some girls who have everything. She has the right clothes, the right friends, and the right last name, but fifteen-year-old Maddie Crane sometimes feels like an outsider in her wealthy seaside town. And when her gorgeous, eccentric cousin Cordelia LeClaire moves to town, Maddie is drawn toward her ethereal, magical spirit and teeters even more toward the edge of her friends' tightly-knit circle...
Then there are the jealous ones. Kate Endicott and the Sisters of Misery - a secret clique of the most popular, powerful girls in school - are less than thrilled by Cordelia's arrival. When Kate's on-again, off-again boyfriend Trevor takes an interest in Cordelia, the Sisters of Misery become determined to make her pay...
Now Maddie must choose between her loyalty to her cousin and the wrath of the Sisters of Misery...
(summary from the back of the book)

This book sent shivers down my spine. I'm always up for reading something out of the ordinary, and according to today's teen literature standards, this is as far from your normal chick lit and beachy romances as you're going to get. And that's not a bad thing, not at all. The thing that attracted me most to the book was how it promised to be something out of my comfort zone. I wanted to read something that would hit me hard and stay with me, and after reading Sisters of Misery, I knew that I got exactly what I had asked for. While there may have been flaws in the book, the addictiveness of the plot was able to overcome that and keep you reading. There were some very confusing parts, sentences with clashing statements, not so well developed characters, and other things like that. Normally, if I came across one of those things in a book it would decrease my opinion of the story automatically. The one reason that didn't happen with this book was because I could dismiss all of the faults because of the fresh and shivery the story had to me. Megan Kelley Hall proved that she can write. I am looking forward to the next book, The Lost Sister, with great anticipation because the end of the book left off with a serious cliff hanger. I'll definitely be reading anything Megan Kelley Hall has to offer in the future as she has made her mark, in my brain at least. I highly suggest that you go out and pick yourself up a copy of Sisters of Misery. It's sure to grab you tight, and keep you guessing until the very last page.