Notes from a Liar and Her Dog by Gennifer Choldenko
Ant (short for Antonia) is sure she is adopted. She doesn't look anything like her mother or her sisters - or even her dad (who is away working too much). Ant's best friend is a boy called Harrison who draws chickens, and her dog Pistachio, a tiny ageing chihuahua, is her constant companion, but she feels that she just doesn't fit in. Ant's life meanders along until one day her lying starts to cause her, and those around her, some rather serious problems. Forced to face up to some of the things she has spent her life trying to hide from, in particular Ant has to come to terms with why she doesn't get on with her mother. This is an uplifting, exciting and truly original story.