Answer: Lucy should specialize in Developmental psychology.
Explanation:
This type of psychology is to study why and how a human can change during the course of their life span.
There are three major issues that is focused on during this psychology. They are psychical, cognitive, and  socioemotional development. Every stage of life is looked at until death. At the beginning of developmental psychology only infancy, childhood, and adolescents were observed, but in modern times all ages are looked at.
This type of psychology was developed by John B. Watson and Jean-Jacques Rousseau in the 18th century.
