Throughout the story, Mansfield employs a distanced and ironic tone which allows her to comment on Miss Brill's behavior and beliefs even as the narrative is firmly rooted in her consciousness.
At multiple points in the story, Mansfield shows Miss Brill passing judgment on old and shabby park visitors with whom she has much in common. Looking around at the other people watching the orchestra play, Miss Brill remarks:
Other people sat on the benches and green chairs, but they were nearly always the same, Sunday after Sunday, and – Miss Brill had often noticed – there was something funny about nearly all of them. They were odd, silent, nearly all old, and from the way they stared they looked as though they’d just come from dark little rooms or even – even cupboards!
It's evident to the reader that in her critical description of others, Miss Brill is essentially summing up her own appearance. Mansfield's pointed interjection "Miss Brill had often noticed" and her use of the somewhat silly exclamation point contribute to an arch tone in this passage; the author is signaling that she and the reader know things about Miss Brill that the character doesn't.
Likewise, Miss Brill's repeated assertions of her own happiness take on an increasingly ironic and even mocking tone as her actual loneliness becomes more apparent. After making an elaborate comparison between the park visitors and the actors of a play, a comparison that is clearly delusional and intended to give her a false sense of belonging, Miss Brill becomes emotional:
Miss Brill’s eyes filled with tears and she looked smiling at all the other members of the company. Yes, we understand, we understand, she thought – though what they understood she didn’t know.
Although the passage employs the stream-of-consciousness technique to capture Miss Brill's direct thoughts, her admission that she doesn't know "what they understood" allows Mansfield to comment on the farcical nature of the entire play comparison. At moments like this, the tone is so ironic that it feels like Mansfield is making a joke at her character's expense.
After the young couple insults Miss Brill, Mansfield's tone becomes even more distanced. The story reports Miss Brill's journey home in sparse, matter-of-fact prose, without providing much access to the character's thoughts. Writing in the last sentence that Miss Brill "thought she heard something crying," Mansfield suggests that the character herself is crying, while also expressing her desire to avoid her feelings at all costs. In this moment, Mansfield achieves supreme distance from her character, just as Miss Brill's alienation from the world around is most evident.