One major arc in the story's character development is how the young tomboy and her Abuelita swap roles as the story progresses. Notice how both the Abuelita and the granddaughter change over the course of the story. You might want to talk about what happens to the granddaughter as she steps into the role of caretaker for her dying grandmother.
The granddaughter is portrayed as a very dynamic character from the instant the story begins. She is lively, extremely active, and a troublemaker. At the beginning of the story, the Abuelita is also strong and dynamic. She is portrayed as a strong caretaker with powerful life-sustaining qualities:
Abuelita made a balm out of dried moth wings and Vicks and rubbed my hands, shaped them back to size, and it was the strangest feeling.
In this moment, Abuelita is healthy and full of vitality. She is in command, and has the ability to restore life.
As the story goes on, we learn that Abuelita is quite ill and only has a few days to live. A role reversal happens. The granddaughter starts to take on the role of caretaker, as her abuelita once did for her:
And so it seemed only fair that these hands she had melted and formed found use in rubbing her caving body with alcohol and marijuana, rubbing her arms and legs, turning her face to the window so that she could watch the bird of paradise blooming or smell the scent of clove in the air.
You can see the arc of the granddaughter character here. In the course of the story, she goes from being a wild young troublemaker to a thoughtful and doting caretaker.
There is some dynamic symbolism going on with the moths, which appear twice in the story. This could be a good focal point for your essay. You could formulate your thesis around the moths and what they symbolize about character development. You could argue that they symbolize death, metamorphosis, or shifting into another plane or phase of existence. You could also examine why they appear in the story when they do.
You might also take a closer look at how the author depicts hands in the story. Whose hands are depicted? When in the story do hands appear, and what are they doing? This might be a good way in if you need to talk about character development as well.