Proof of Forever, by Lexa Hillyer

Two years after the last summer that Zoe, Joy, Tali, and Luce spent at camp together, they come back for a campers' reunion.  That last summer had been very special, but they have long since moved on.  Seeing each other is awkward and each of the girls is dealing with issues of their own that distract them from enjoying seeing each other again.

But then a freak incident in a photo booth transports the four girls back in time to that summer two years ago.  And they find themselves in a week-long do-over.  At first, they are convinced that they must reenact the past exactly how it originally happened.  But it quickly becomes apparent that not only do they not remember the past well enough, but that things are different this time around.  Or perhaps, it is they that are different?  In the process of reliving the most memorable week of their lives through their older and wiser selves, they discover that what they remember and what actually was going on are entirely different things .

I loved the idea of a story which combined summer camp fiction with the buddy girl story (the blurb hypes this as the new Sisterhood of the Traveling Pants) and threw in a little time travel to boot.  Admittedly, the time travel is the weakest part of the story -- it's poorly explained and makes little sense -- but since it is not essential to the story, it can be easily forgotten.  The girls are all interesting and the process of discovery through a critical reexamination of their past was lots of fun.  I was less taken with the plot's slow pacing (the ending really did seem to drag -- there were simply too many events -- talent show, fencing competition, scavenger hunt, etc. to get through).  It could have been trimmed down a lot!