Rose McIver has been working since age 3, thanks to commercials and TV shows in her native New Zealand, as well as two Disney Channel movies but she's never been someone you'd recognize on the street. Well, she's about to find out what a difference one role can make. The actress, 21, has a pivotal part in The Lovely Bones, Peter Jackson's adaptation of the riveting 2002 novel, which hits theaters Dec. 11. She plays Lindsey, the inquisitive younger sister of the teenage Susie (Saoirse Ronan), a murder victim watching over her family from the afterlife. ''It was one of the first books I read with such complex subject matter,'' says McIver, who discovered the novel at 13. To play Lindsey, the actress had to channel her inner teenager. ''We shot out of sequence, so one day I might be playing 12 in the morning, 15 in the afternoon, and 19 in the evening. But I've had all of those experiences. It wasn't like I was trying to play a 50-year-old!'' McIver, a psychology and linguistics major at New Zealand's University of Auckland, seems poised for a great acting career she's also shot a crime comedy called Predicament. But she won't be distracted by fame: ''I've got exams next week, so that's keeping me plenty busy.''