Curley's wife, because she is the spouse of the son of the ranch owner, tries to lord it over the ranch hands, revealing her arrogance and a lack of sensitivity for their feelings. And although Candy and Crooks try to warn her that she shouldn't toy with Lennie, whose behavior can be unpredictable because of his mental disability, her arrogance causes her to disregard their advice, leading to her death.
Curley's wife, though clearly unhappy, comes across in the novel as a petty person. For example, she abuses her power as a white woman over the black Crooks, threatening to say that he made a sexual overture towards her to reduce him to a state of humiliated servility, a petty gesture on her part. Instead of feeling sympathy for her husband's crushed hand, she is glad he got hurt, another instance of her pettiness.
Curley's wife is an angry and disappointed woman, who feels disregarded by her husband and isolated as the only female on the ranch.
A feminist reading might fault Steinbeck for creating so relentlessly unpleasant a female character as Curley's wife, but a defense could be that Steinbeck sees her too as a victim of a social order that encourages some to feel superior to others merely on the basis of having a little more money.