I would suggest that Erica's fate was to be the kind of person who was fundamentally "alone in a crowd."  Changez notes this about her from almost the beginning of their interactions.  Erica was always on the edge socially and while it seemed like she had nearly everything in her possession, her fate was to suffer a condition of hollowness within her that would eventually take her as its victim.  Erica was open about her feelings regarding Chris and the fact that she never quite was able to overcome his absence.  In this respect, her feelings towards Chris become the one element of her undoing.  After the attacks of September 11, the feelings of insecurity and doubt are too strong for her and coupled with her sensitive experience about Chris, Erica is plunged into a major depression.  Her nostalgia about living a life with Chris is her last stand to try to establish some premise of happiness in an existence that ends up becoming victimized by the inability to understand the past in the context of the present and the future.  When she takes her own life, it becomes the stunning reminder that the inability to properly understand the past and present has a tremendous impact on one's future.  Erica's fate is to be the living embodiment of William Faulkner's idea that "The past isn't dead and buried.  In fact, it isn't even the past."  It becomes a sad irony that Erica, an American who had nothing but the future in front of her, could not overcome her own past and embrace what was there, potentially waiting for her.