What I remember the gist of the story being is that there was this girl, and that her parents decided it would be best if she were left in her grandmother's (I think) care. They had to drive several states away to get there and then the parents leave without any indication of when they'll be back or where they're going.
Fast-forward a bit, and it turns out that this girl is a clone of her parents' first daughter, who died 16 years ago. This lines up with the girl approaching her 16th birthday and thus nearing the age that her sister got killed in a car crash (it had something to do with a car at least; I'm not sure if it was a crash or if she just fell out). Anyway, the girl wants to separate herself from this identity, so when her grandmother tries to give her peach-flavored cereal, the girl simply states that she doesn't like peach and asks for something else.
I can't remember anything else or how it ends, but I think it came out after 2000, just not sure when exactly. I read this in fifth grade so it's been a while to say the least.