Tainted

Im trying to find a book that I read back in middle school. I can't remember much but there is a character who the MC likes and goes by O.
Also i believe the MC was in rehab or something because she comes back and finds out a girl who was dead is alive, also I believe that was part of why she went to rehab
The sister made a deal with the lake to take the girl, instead of the MC, who was the one who originally died
Fast forward
The the MC goes to the lake because of O
And then the sister comes to the rescue and since the lake originally wanted the MC, the sister dressed up as the MC and the lake takes the sister

The last chapter is about how the MC now visits the lake daily to talk to the sister and the town people start to call her crazy

Also there is one scene where the girl is driving O out of town and since she's dead she technically can't leave the town so she literally vanishes and O gets in an accident and gets a arm cast

I can't remember the name of anyone besides O
Also hope that made sense and hopefully this rings a bell to someone because I've been looking for this book for years

And I know it's not manga related but if anyone reads books who could help

http://www.mangago.me/read-manga/gintama_dj_mienai_kusari/