Read a chapter of it in 2011, it was a thriller. I initially thought it was by Karin Slaughter but seems not, I'm almost certain it's a female writer.
It involved a teen/young adult girl. She had a scar on her face from a previous accident which may have involved swimming and may have been a setup. Almost certain there's a sister who has some suspect friends and at beginning of the book they were on a yatch/boat.