The death of Curley's wife could be said to symbolize the ultimate futility of dreams. Like just about everyone on the ranch Curley's wife has her dreams: in her case it's to make it as a movie star. But her dreams end up dashed just like everyone else's, and as with everyone else in the story, her dreams are dashed through no fault of her own. The death of Curley's wife in turn leads to the end of George and Lennie's dream to own a ranch, a dream which also involved Candy.

Despite the United States being in the grip of the Great Depression the national myth of the American Dream still exerted a powerful hold on the public imagination. But in the fate of Curley's wife Steinbeck appears to argue that the American Dream and all it represents holds out a false hope of self-improvement for those who wish to escape their spiritually and materially impoverished lives.

Curley’s wife’s death is a symbol of loss of innocence.

The death of Curley’s wife is a very sad time in indeed. She does nothing wrong, and Lennie kills her accidentally. Her death is therefore a tragedy, and symbolizes the end of Lennie’s carefree life. Although Lennie does not necessarily become a bad person after killing her, we can no longer think of him as a harmless man-child. He proves to be dangerous.

Her death also serves as the end of the innocent part of the story. Although things were not all roses before Curley’s wife dies, George and Lennie were moving along and doing fairly well. Their life was about survival, but centered around the innocent dream of the rabbits. After Curley’s wife is killed, there is no way George and Lennie can exist peacefully and continue their lifestyle. George has to put Lennie out of his misery.

What does Curley's wife in Of Mice and Men represent?

I think that Curley's wife can be seen to represent a couple of elements.  One would have to be the painful weight of dreams.  Curley's wife represents what happens when dreams fail and the burden this weight places on the individual.  Her entire being is rooted in the idea that she could have been something more than she actually is.  In this, Curley's wife is representative of the not only the death of dreams and the personal, stinging failure this causes, but also what happens when individuals must live with their own futility.  Her desire and hopes to be in "pitchers" collide with being the only woman on this ranch, a collection of others whose failures represent the sum total of their own consciousness.  In this, she represents what it means to both fail and how pain- ridden consciousness is when one lives with this.  I think that this becomes one of her primary functions in the novella.  Her entire moment with Lennie is a moment to be admired and to be loved, like she would have been on screen had she been an actress in "pitchers."  It only makes sense that this would be the instant that ends up killing her, a reminder that the pain of failed dreams can be a form of death in its own way.