'My Sister's Keeper,' an adaptation of the novel by Jodi Picoult, has to do with emancipation, a theme that the movie itself unwittingly plays into. Within this structurally baggy weepie, at least two perfectly good movies fight to break free, one a provocative legal thriller, the other a melodrama. If director Nick Cassavetes had decided to make just one of those films, 'My Sister's Keeper' would have provided a nifty piece of counterprogramming to the fare on most screens. He did succeed in creating an adaptation that, although departing dramatically from such key elements as the book's ending, will please fans. Anna (Abigail Breslin) is an 11 year old conceived by her parents (Cameron Diaz and Jason Patric) in order to harvest umbilical-cord blood, bone marrow and various organs for their daughter Kate (Sofia Vassilieva), who has leukemia. Anna has hired an attorney (Alec Baldwin), demanding to be 'medically emancipated' from her parents -- she doesn't want to donate the kidney she was bred to give up. As long as the movie stays with that issue, it toggles smoothly between intellectual arguments and rank emotionalism. But then the focus turns to Kate's story, when she meets a fellow patient and falls in love. It's an undeniably affecting sequence, but it represents one of several tonal shifts that make the film an ever-widening shaggy dog story. Breslin and Vassilieva acquit themselves beautifully. Diaz plays their mom with a careworn absence of vanity. Perhaps a moment of silence is in order to recognize the fact that one of Hollywood's most delectable pop tarts is playing the mother of teen-agers (meaning I must be 100 years old). Sic transit gloria mundi -- yet another theme of one of the many movies that make up 'My Sister's Keeper.' 'My Sister's Keeper' PG-13, 109 minutes Contains mature thematic content, disturbing images, sensuality, profanity and brief teen drinking. 