In "Where Are You Going, Where Have You Been?", if Connie were your sister and you could foretell what was going to happen (but you still have to leave her alone), what would you do to help "save" her?
In a sense, Connie's fate derives both from her character and her environment. First, she is detached from her family life, almost sleepwalking through her adolescence. While she enjoys popular culture and shopping, and is experimenting with sexual relationships with boys, she seems ultimately without deep roots, connections, or aims. We get no sense of her being deeply committed to any creative activities or career goals. She's not involved with a church or any charitable or political causes, and she doesn't seem to be particularly close to her family. This lack of direction, commitment, and communal bonding makes her susceptible to the man in the car.
If you were Connie's sister, you might try to help her find some goals in life that are deeper and more meaningful than just hanging out at the mall. You could also talk to her more, and help her stay closer to her family and more involved in family activities. If she had a happier, more meaningful life, she probably would be less likely to run off with quasi-strangers.