How can a sunny, impossibly efficient teen created in 1930 fit into a modern movie? By being an alien anachronism to her peers, with not just the penny loafers but the cheery spunk. It helps that the sleuthing heroine of 175 books is played by Emma Roberts (Eric's daughter, Julia's niece). At 16, she's splendidly free of the usual adolescent attitudinizing. Andrew Fleming's movie is sloppy and subpar, but Emma is so poised, so persuasively genuine, she could be a Jane Austen heroine.