Conclusion of why Esperanza says Nenny isn't her friend?

In the chapter, Boys and Girls, we are introduced the gender separation dominating the narrator's social and cultural experience. We learn that outside of the home, brothers Carlos and Kiki are comrades, while the narrator and sister Nenny are playmates. The narrator then expresses dissatisfaction at being paired with her sister, who is "too young to be my friend." It is the narrator's responsibility to not only play with her sister, but to watch over her so that she isn't influenced by the wrong crowd, such as "those Vargas kids." The narrator ends the chapter with a wish for her own best friend who will sympathize with her secrets and laugh at her jokes.