Final answer:
A teen acting for the betterment of the overall population, despite the choice being unpopular, demonstrates post-conventional moral reasoning, as per Kohlberg's theory.
Step-by-step explanation:
When a teen chooses to do something unpopular, but it serves the betterment of the overall population around her life, she is displaying post-conventional moral reasoning. This level of moral reasoning is characterized by understanding morality in abstract terms and recognizing that legality and morality may not always coincide. Kohlberg's theory of moral development identifies this stage as one where individuals make decisions based on principles that reflect universal ethical principles, rather than conforming to societal norms or personal gains.