The False Friend by Myla Goldberg

Okay, here's the simple setup: two eleven-year-old girls, best friends yet fierce rivals, go into the woods. Only one comes out...
However, this novel is not simple at all. 20 years later, Celia Durst decides it's time to tell the truth about what really happened all those years ago. That is not as easy as it seems. There are many obstacles and twists and turns along the way as The False Friend slowly builds to the climax.

Karen