Alienation
Miss Brill is a supremely alienated character. She is alienated from the world around her. She even seems to suffer from self-alienation as she does not appear to be fully in touch with the reality of her own appearance or the image that she presents to the world. She is literally a foreigner, teaching in France though she is English, and she does not seem to have any close intimates. Alienation was a common theme of the Modernists, who sought to depict individual lives like Miss Brill's or Eliot's Prufrock in order to comment on how modern life's fragmentary nature precluded deep connections and self-awareness.
Disconnect between Fantasy and Reality
Miss Brill’s construction of an invented narrative for the park visitors that takes the form of a play enacted for her sole benefit becomes a metaphor for her entire life. Everything is an illusion and a fantasy because she has become disconnected from what is real. This alienation from reality is in part a defense mechanism to deal with her loneliness, but it also serves as a corollary to her conscious disengagement from a real life that involves real interaction with others. Just as most people realize that it is impossible to actually interact with characters on a stage or screen, so Miss Brill’s construction of a fantasy life fulfills the purpose of allowing her the excuse for disengagement; the people making up the cast of her interior plays are nothing more than phantoms on celluloid.
Public and Private
Though most of the action of this story takes place in public, there is still an evocation of the private. First of all, Miss Brill sits in the gardens and watches all manner of people come by. She is literally in a public place and decides that she is an integral part of that space. However, Miss Brill is actually in a private space of her own making, characterized by unreality and mutability, and when the public space that she thinks she is a part of intrudes on that private world (via the young couple speaking rudely about her), she is discombobulated and traumatized.
