When Curley’s wife is first introduced, she blocks out the sun. When she is dead, the setting sun is high and growing soft. The sun is a metaphor for her bright life being ended, or the sun setting on her life.
Curley’s wife is introduced with a ray of sunshine. When Lennie and George first meet her, she blocks the sun with her presence.
Both men glanced up, for the rectangle of sunshine in the doorway was cut off. (ch 2)
When the girl is described, she is described with bright colors and strong images.
She had full, rouged lips and widespaced eyes, heavily made up. Her fingernails were red. Her hair hung in little rolled clusters, like sausages. She wore a cotton house dress and red mules, on the insteps of which were little bouquets of red ostrich feathers. (ch 2)
The red fingernails, shoes, and ostrich feathers are all bright, like the sun.
After Lennie accidentally kills her, those sparks of life are gone. The metaphorical sun is setting.
The sun streaks were high on the wall by now, and the light was growing soft in the barn. Curley’s wife lay on her back, and she was half covered with hay. (ch 5)
As the description continues, it is noted that “the meanness and the plannings and the discontent and the ache for attention were all gone from her face” (ch 5). Death seems to have reduced her to her pure self.
She was very pretty and simple, and her face was sweet and young. Now her rouged cheeks and her reddened lips made her seem alive and sleeping very lightly. The curls, tiny little sausages, were spread on the hay behind her head, and her lips were parted. (ch 5)