Final answer:
Sophie made friends with Agatha because she was lonely and saw Agatha as a potential companion. These relationships serve to drive the narrative and character growth, reflecting the realism of transient human connections in life.
Step-by-step explanation:
Sophie made friends with Agatha in the first place because she was lonely and saw Agatha as a potential companion. In the text, it is mentioned that Sophie was interested in Agatha because she found her charming, and believed that they could enjoy each other's company.
Sophie also mentioned that they could always leave each other if they got tired of each other, indicating that their friendship was not based on deep emotional connection, but rather, convenience.