When we look at poetic devices in the narrative of the story Her First Ball the most salient one is definitely imagery. Imagery is the license used by writers to appeal to all the five senses so that the reader can become immersed in the work.
In this story, the main character is experiencing a first major event Her first ball. It is necessary that Mansfield describes all her emotions by summoning every sight and sound that helps the main character connect to her environment and completely convey her atmosphere onto the reader's own:
Darling little pink-and-silver programmes, with pink pencils and fluffy tassels
The use of similes helps to also establish comparisons between the main character's feelings versus what is really going on:
the bolster on which her hand rested felt like the sleeve of an unknown young man's dress suit; and away they bowled, past waltzing lamp-posts and houses and fences and trees.
Even the things she remembers from before her first ball (which is used to establish a dramatic contrast between the past and the present) pay tribute to all the senses:
that dusty-smelling hall–with calico texts on the walls, the poor, terrified little woman in a brown velvet toque with rabbit's ears thumping the cold piano.
We can also find onomatopoeia and personification when Leila remembers the sounds of her country home
she had had to be sitting on the veranda of their forsaken up-country home, listening to the baby owls crying "More pork" in the moonlight
You can find a myriad of poetic devices used in Her First Ball. Mansfield treated with great care and detail the themes of innocence, naivete, and the old versus the new. Almost the entire story is literally soaking with detail and depictions, emotions, and observations. Conclusively, the use of imagery is the strongest stylistic device and certainly the one which conveys the strongest sense of poetry within this prose work.