How is Miss Brill a Cheerful Optimist?

This story by Mansfield encourages confusion about Miss Brill because of its loose-jointed, rambling psychological discourse. However, careful consideration of the text illuminates the character of Miss Brill. Two questions the text helps us focus on are "Is her life pathetic?" and "Why does she want to shake the lady talking pessimistically about eye glasses?"
Is Her Life Pathetic?
Miss Brill leads an unornamented life but maintains a cheerful optimism nonetheless. She takes delight in the simple pleasures available to her. She doesn't sit on her red eiderdown in her small room bemoaning her misfortune. Instead she ventures out; she enjoys what is available to her, even the chill of the air; she finds companionship of sorts where it can be found. Miss Brill's optimistic and cheerful life cannot be called pathetic.
There are a few things Miss Brill does that raise her existence above the pathetic. Living in France, she teaches English and chats with her students, creating relationships even though they are defined by the exchange of services and payments. She takes care of and takes pleasure in her modest possessions which, though reflecting an earlier epoch, signify a social class above her present one, similar to Miss Bates in Austen's Emma. She takes herself to the park on Sundays during the concert season to listen to the band and to "people watch," a time honored recreation. Though she doesn't know them, she takes a lively and imaginative interest in the other people who frequent the park concerts. She treats herself to the fun of a Sunday honey-cake to eat with her afternoon tea.
[When there] was an almond in her slice. . . [s]he hurried [home]. . . and struck the match for the kettle in quite a dashing way.
The joy, delight and optimism with which she undertakes each of these simple actions betells a life that is above the pitiable, above miserable, and above the pathetic. Her little fur necklet, then fashionable and equivalent in price to an autumn coat, and her eiderdown, an elegant type of feather comforter plucked from the breast of the eider duck, bespeak of a wealthier, happier earlier existence, but continue to give her cheer and courage rather than bitter regret. Miss Brill does not feel her life to be pathetic at all.
Why does she want to shake the lady talking pessimistically about eye glasses?
Miss Brill is an optimist. Miss Brill knows how to undertake action to gain what will benefit her. More importantly, she knows when something will benefit her, like fresh air, band music, a Sunday tea-cake, a soft fur at her neck. The eye-glass woman in the park needed a good shake, in Miss Brill's opinion, because she was a complaining pessimist; she could not take action for her benefit; she could not even tell what would benefit her. Miss Brill wanted to shake some sense into her so that she would see life as an offering of possibility rather than as a slough of brokenness; she wants the woman to take action and be a grateful optimist.