Alison, Who Went Away — Vivian Vande Velde

Fourteen-year-old Susan (or, as she prefers to be called, Sybil) has been trying to reinvent herself ever since the mysterious disappearance of her older sister, Alison. Life has been very confusing since Alison left. Susan's mother has become overly protective, fearful of losing another child. Her new school is not all bad, of course, but it is different and puzzling. Her best friend, Connie, has what could be a wonderful idea  -- or maybe it has the makings of a disaster: if they sign up for the school play, they might end up with dates for the freshman dance.
Readers will empathize with Susan's attempt to make sense of her confused world, the loss of her sister, a new school, turmoil at home, and the growing pains of adolescence. But Susan, despite all, remains bright, funny, and self aware with the help of a new and intelligently supportive stepfather and a lively group of school friends. The story is believable and touching and distinguished by the narrator's voice.