Final answer:
The social worker should next obtain a release from the mother to speak with the school counselor to better understand the girl's bullying behavior in the school context (option B).
Step-by-step explanation:
After completing a social and developmental history with the mother regarding her daughter's bullying behavior at school, the social worker should next have the mother sign a release to speak with the school counselor. This step is pivotal because it allows the social worker to gather more context and insight from the school environment, which differs from the home and apartment complex setting where the daughter reportedly gets along well with her siblings and other children. Understanding the school dynamics will contribute to a more comprehensive assessment of the girl's behavior and help in planning appropriate interventions for the bullying issue.
Hence, the answer is option B.