Fans of Jodi Picoult, Caroline B. Cooney, and Lurlene McDaniel--teens and adults alike--will relish this emotional roller coaster ride of a novel.     When Rosie's mother, Trudie, dies from Huntington's disease, the girl's pain is intensified by the knowledge that she has a 50 percent chance of inheriting the crippling disease herself. But when Rosie tells her mother's best friend that she is going to be tested for the debilitating illness, Sarah, a midwife, reveals that Trudie wasn't her real mother after all. Rosie was swapped at birth with a sickly baby who was destined to die.     Devastated, Rosie decides to join her ex-boyfriend on his gap-year travels, leaving England to track down her birth mother in California. But all does not go as planned. In America, Rosie discovers more of her family's long-buried secrets and lies, and she is left with an agonizing decision of her own--one that will be the most heartbreaking and far-reaching of all.