Marta is a rebellious teenager. Shane's mom does not want Shane to spend time with Marta because she is worried Marta will make Shane break the rules at home, just as Marta does at her home. Shane's mom is worried about the bad apple effect.

Bad Apple Effect

A phenomenon where the negative attitudes or behaviors of one member can spread and influence the entire group.

Rebellious Teenager

A young person in the phase of adolescence who rejects established norms and seeks autonomy, often leading to conflict with authority.