Curley’s wife presents a threat to Candy. Her insistence on socializing with the men puts them in a potentially disastrous position (and at least an awkward one). She also displays some lascivious tendencies that contribute to the air of danger surrounding her on the ranch.
Perhaps most importantly for Candy, Curley’s wife casts doubt on the validity of the plan to collectively band together to purchase property. This dream, shared with George and Lennie, is disparaged when Curley’s wife hears about it. She expressed disbelief and suggests that this group is incapable of such an achievement. This challenge Candy’s pride and his hope becomes part of any calculation as we try to assess why he might cling to the idea that Curley’s wife is a tart.
Rather early in the book, Candy tells George and Lennie to watch out for Curley’s wife because she seems to be actively trying to get the ranch hands into trouble. She flirts with Slim, according to Candy, and acts ambiguously toward George. George is wary of her, in part probably because he worries about Lennie’s troubled past with young women, but also because he can see that she is willing to cross social boundaries in ways that may endanger a ranch hand’s job - - or worse.
While Curley’s wife confesses to Lennie about her past and her present isolation on the ranch, becoming a sympathetic character, she seems to have very little social tact. Her lack of communication skills challenge her ability to convey her true and mostly innocent intentions to the ranch hands like George and Candy.
Consequently, Candy’s reasons for fearing and resenting Curley’s wife are never alleviated. When he finds her dead body, Candy realizes that she has effectively succeeded in killing his dream of buying a ranch with George and Lennie. The threat that she posed has materialized.
“You God damn tramp,” he said viciously. “You done it, di’n’t you? I s’pose you’re glad. Ever’body knowed you’d mess things up. You wasn’t no good. You ain’t no good now, you lousy tart.”
Though she is dead, Curley’s wife has committed a final act of harm to Candy, as he must see it.