The most pronounced element of Mansfield's style is the close proximity of the involved, subjective narrator. Narrators may be distanced or close in proximity, as they may be objective or subjective. Most often, a distanced narrator tends to be an object one while a close narrator tends to be a subjective one. Narrators may also be involved or uninvolved with the action and characters of the story. An involved narrator doesn't comment upon characters or events while an involved narrator does comment. For example, Hemingway is often categorized as having an uninvolved narratorial voice that refrains from comment and judgement (as an aside, upon consideration it may be argued that his narrators are actually deeply involved though reticent). On the other hand, Jane Austen has a very involved narratorial voice that relishes commenting through her famous ironic voice.
Mansfield's narrative style employs a narratorial voice that is in close proximity to the action and characters. This is established in the opening line in which the narrator is close enough to begin with telling us Leila's thoughts: "Exactly when the ball began Leila would have found it hard to say."
The narrator's voice is also subjective, that is, the narrator comments on events and characters from a private, personal observation, judgement, and reflection. In the case of Mansfield's narratorial style, this subjective narrator is favorable toward Leila, so the narratorial comments are kind and informative: "if it hadn't been impossible, she couldn't have helped crying because she was an only child, and no brother had ever said "Twig?" to her; ...."
The narrator's voice is also involved, which means it comments with enthusiasm. An example is the comment the narrator when Leila is first traveling to the ball. The narrator comments with an exclamatory before using indirect speech to let us know what Leila is thinking and doing: "Oh dear, how hard it was to be indifferent like the others! She tried not to smile too much; she tried not to care ...."