In Steinbeck's Of Mice and Men, we first hear about Curley's wife from one of the ranch hands. She is never given a name, which may show that Steinbeck includes her mostly to move the plot along. The man says:
"Wait'll you see Curley's wife."
..."Purty?" [George] asked.
"Yeah...Well—she got the eye."
"Yeah? Married two weeks and got the eye?..."
..."I've seen her give Slim the eye...Curley never seen it. An' I seen her give Carlson the eye."
...The swamper stood up from his box. "Know what I think?...I think Curley's married...a tart."
The swamper is saying that Curley's wife is always eyeing up the other men, and she's only been married two weeks. He believes she may be a "tart" or a prostitute. The reader's initial sense is that Curley's wife is one to stay away from if George doesn't want trouble with the boss's son.
When Lennie and George first see Curley's wife, she shows up at the bunk house.
She had full, rouged lips and wide-spaced 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.
She is not dressed as a woman living on a ranch should dress, especially when she is around men—especially as there are no other women living on the ranch. She looks like she wants attention from the way she is made-up. And though her husband has told her to stay away from the men, she does not listen.
Curley's wife is obviously a little frightened of her husband. At one point when she says she is looking for him and is told he just went into the house, she leaves quickly.
George is aware early on that she is dangerous.
She's gonna make a mess. She's a jail bait all set on the trigger. That Curley got his work cut out for him. Ranch with a bunch of guys on it ain't no place for a girl, specially like her.
At one point after Curley tries to beat Lennie up, Curley's wife shows up at the bunk house again, "looking for Curley," who is obviously not there.
...I ain't giving you no trouble. Think I don't like to talk to somebody ever' once in a while? Think I like to sick in that house alla time?
Curley's wife may be lonely, but the men know enough to stay away from her. She won't leave, but announces that she doesn't care much for her husband and is sure his hand was broken because he picked a fight. She can also be nasty. When Crooks (who is black and works on the ranch) tells her to go, she gets mean and infers that he should shut up, or she can make an accusation that will get him lynched.
By the end of the story, Curley's wife finds her away to Lennie, trying to talk with him. He tells her to go away because he isn't allowed to talk to her. She dismisses George's warning:
He's scared Curley'll get mad...
She uses these words to convince poor Lennie that there is no reason he cannot speak to her. And though he tries repeatedly to resist, she will not go away. She takes Lennie's hand and puts it on her hair because he likes soft things, but when he won't let go, she gets frantic. To keep her quiet, Lennie puts his hand on her mouth and accidentally kills her.
Had she stayed away from the men like Curley had told her, she would have been safe.