Then, the sugar plum fairies appear, through an ornamental pattern of piqué turns, until they are stopped in their tracks by Edgars, puffed with pride in his Mouse King costume.
The way the author writes this sentence/imagery allows the reader to imagine the scene in their head clearly.
I know, she also likes Edgars, who is not afraid of making mistakes and who can arabesque higher than maybe I ever will despite his shiny pants and flat black slippers and the fact that he is a boy and should be doing something else besides dancing.
The author shows her frustration that a boy who shouldn't even be dancing can arabesque higher than her and how she despises Edgars and his shiny pants and black slippers(imagery).
I should be a sugar plum fairy in a pink tutu with red rouge-smears on my cheeks.
This sentence contains imagery as it describes what the sugar plum fairies look like with their pink tutus and rouge.
Then, Diana, who is playing Clara but who is really a perfect ballerina beneath her green velvet dress and doilie collar,
The author uses imagery by using detailed descriptions to paint an image of Diana's dress in the reader's head. The author goes into detail of the color, material, and collar of Diana's dress.
I count the moles on Miss Erika’s back, round and raised like licorice drops,
There is imagery as the author uses figurative language to describe the moles on Miss Erika's back looking like round bumps that look like licorice drops.