Reena is the 12-year-old narrator and protagonist of Moo. She has lived all of her life in New York City and views herself as a city girl, but she is excited to move to Maine and try living in a new environment. Reena is often the spark for ideas within her family: She suggests Maine as a new home, and she is the one who solves the problem of how to care for Mrs. Falala’s animals after Mrs. Falala’s death. She is a loving and protective sister to her younger brother, Luke, and a respectful child who cares deeply about her parents’ opinion of her. She is compassionate toward animals—it is Reena, for example, who first understands that Zora is lonely—and sensitive to the beauties of the natural environment.

Reena is also a dynamic character who grows and changes over the course of the novel. The relocation to Maine removes her from the urban environment she is used to. Although there are things that she appreciates about the city, she is also tired of the noise, the traffic, and the crowds, and she is ready for a new adventure. Initially, she worries about how she will fit in, and she struggles to even speak in the presence of Maine natives like Zep and Beat.