Between the Lives by Jessica Shirvington

For as long as she can remember, Sabine has lived two lives. Every 24 hours she Shifts to her 'other' life - a life where she is exactly the same, but absolutely everything else is different: different family, different friends, different social expectations.In one life she has a sister, in the other she does not. In one life she's a straight-A student with the perfect boyfriend, in the other she's considered a reckless delinquent.Nothing about her situation has ever changed, until the day when she discovers a glitch: the arm she breaks in one life is perfectly fine in the other. With this new knowledge, Sabine begins a series of increasingly risky experiments which bring her dangerously close to the life she's always wanted...But just what - and who - is she really risking?