Saving Zoe by Alyson Noel
Just days before Echo's fourteenth birthday, her older sister Zoe was brutally murdered. Now as Echo is approaching her fifteenth birthday she is working through the various steps of grief, trying to be patient and understanding with her zoned out mom and absent dad, and deal with all of the stares, gossip, and comments that come with being the "tragedy girl." The stares and comments have only gotten worse now that Echo is beginning high school where she has to come face to face with Zoe's friends and boyfriend, Marc, each day. Then Marc offers Echo her sisters diary to read. Reading Zoe's diary helps Echo get to know Zoe, the real Zoe, and also gives her clues as to what exactly happened that led up to her being brutally murdered.
I thought this was a really good book. And even though it involves a lot of heavy duty mature themes (murder, sex, drugs, date rape) as a few unfair reviews point out, the book never goes into great detail on these points.