John Steinbeck's classic Of Mice and Men was set in the 1930s, and that is important context to note when considering quotes that show that Curley's wife is powerless and regretful. Women in the US in the 1930s only had the right to vote for a decade and were only allowed to divorce if they could prove abuse or abandonment. These were known as fault-based divorce laws. Women were generally not allowed to get loans on their own and were for the most part financially dependent on their husbands.

Considering this context, readers can see that any hint of unhappiness would leave a woman feeling quite trapped in this period of time. The first hint that there is trouble in Curley's marriage comes shortly after George and Lennie arrive at the ranch. The old swamper is telling them about how things are at the ranch and reveals to George that he thinks Curley's wife has a wandering eye. Here's a quote:

"Yeah? Married two weeks and got the eye? Maybe that’s why Curley’s pants is full of ants."
"I seen her give Slim the eye. Slim’s a jerkline skinner. Hell of a nice fella. Slim don’t need to wear no high-heeled boots on a grain team. I seen her give Slim the eye. Curley never seen it. An’ I seen her give Carlson the eye."
George pretended a lack of interest. "Looks like we was gonna have fun."
The swamper stood up from his box. "Know what I think?" George did not answer. “Well, I think Curley’s married...a tart."
"He ain’t the first," said George. "There’s plenty done that."

A "tart" was a slang term for a promiscuous woman or a prostitute. That's a pretty serious allegation to level at Curley's wife, but consider that the social standards were quite different then, and any woman who was boldly flirting or giving suggestive looks to men would have been a bit scandalous, let alone one who was married.

Candy has the temerity to confront her about her inappropriate behavior, including dressing and moving provocatively and always looking for attention from the men. She replies:

“Well, 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 stick in that house alla time?”
Candy laid the stump of his wrist on his knee and rubbed it gently with his hand. He said accusingly, “You gotta husban’. You got no call foolin’ aroun’ with other guys, causin’ trouble.”
The girl flared up. “Sure I gotta husban’. You all seen him. Swell guy, ain’t he? Spends all his time sayin’ what he’s gonna do to guys he don’t like, and he don’t like nobody. Think I’m gonna stay in that two-by-four house and listen to how Curley’s gonna lead with his left twicet, and then bring in the ol’ right cross? ‘One-two,’ he says. ‘Jus’ the ol’ one-two an’ he’ll go down.’"

This hints at the regret she feels at marrying Curley and also hints at her lack of power to change her situation. Later, she explains to Lennie why she married Curley in the first place. It's a sad story, really: she wanted to be an actress, but her mom forbade her due to the fact she was only fifteen. In an act of rebellion, she met and married Curley. She could not have known him at all, and she is now suffering the consequences of her rash decision. Here is what she reveals to Lennie:

"I tell you I ain’t used to livin’ like this. I coulda made somethin’ of myself.” She said darkly, “Maybe I will yet.” And then her words tumbled out in a passion of communication, as though she hurried before her listener could be taken away. “I lived right in Salinas,” she said. “Come there when I was a kid. Well, a show come through, an’ I met one
of the actors. He says I could go with that show. But my ol’ lady wouldn’t let me. She says because I was on’y fifteen. But the guy says I coulda. If I’d went, I wouldn’t be livin’ like this, you bet.”

Well, I ain’t told this to nobody before. Maybe I oughten to. I don’ like Curley. He ain’t a nice fella.” And because she had confided in him, she moved closer to Lennie and sat beside him. “Coulda been in the movies, an’ had nice clothes—all them nice clothes like they wear. An’ I coulda sat in them big hotels, an’ had pitchers took of me. When they had them previews I coulda went to them, an’ spoke in the radio, an’ it wouldn’ta cost me a cent because I was in the pitcher. An’ all them nice clothes like they wear. Because this guy says I was a natural.” She looked up at Lennie, and she made a small grand gesture with her arm and hand to show that she could act. The fingers trailed after her leading wrist, and her little finger stuck out grandly from the rest.

Her lack of power was due to the time period and her abusive, jealous husband. It also came because of her desperation—she married Curley in a desperate attempt to get away from her mother's rule. Her regrets are many—she regrets not being able to fulfill her dream of being an actress, and she regrets her rash decision to marry Curley, which has given her a lonely and miserable life.

The low self-esteem of the character of Curley’s wife in Of Mice and Men is partly conveyed by her name never being given. She seems to exist as Curley’s accessory and, through his excessive jealousy, he seem to treat her as his property. In her conversations with the ranch hands in the bunkhouse, Curley’s wife speaks frequently about her regrets. These center on marrying Curley. She claims to dislike him because he “ain’t a nice fella.” She complains on two occasions about giving up her dreams of acting in movies:

I tell ya I could of went with shows. Not jus’ one, neither. An’ a guy tol’ me he could put me in pitchers.

[...]

Coulda been in the movies, an’ had nice clothes—all them nice clothes like they wear. An’ I coulda sat in them big hotels, an’ had pitchers took of me.

The question of power is somewhat more complex. Curley’s wife feels powerless because, without a car of her own, she is trapped on the ranch and even expected to stay in the owner’s house. This lack of power is manifested in her resentment when she speaks to the ranch hands when visiting the bunkhouse. She asks rhetorically,

Think I like to stick in that house alla time?

Later, she insults them even as she goes out of her way to visit them.

What am I doin'? Standin' here talkin' to a bunch of bindle stiffs—a n****r an' a dum-dum and a lousy ol' sheep—an' likin' it because they ain't nobody else.

She also understands that she is attractive, so she uses this attribute to stimulate male desire for her. The negative side of this power is her knowledge that by seeming to encourage the ranch hands, she can also stimulate Curley’s jealousy, which could lead to violence or a hand getting fired. Candy calls her “a tart,” and George tells Lenny that she is “a tramp” and “jail bait.” When Candy flatly tells her not to bother them, he shows the limits of her power.

You ain’t wanted here. We told you you ain’t.…You ain’t got sense enough in that chicken head to even see that we ain’t stiffs. S’pose you get us canned.

She later threatens to make trouble for the only Black hand, Crooks, and even threatens to get him lynched. Candy sticks up for him, saying that if she spread lies,

We’d tell about you framin’ Crooks.

Several major details in addition to specific quotations illustrate Steinbeck's theme that women during his time were often powerless and isolated simply because of their gender.

1. Unlike Crooks who is isolated because of race, Candy who is isolated because of his age and injury, and Lennie who is isolated because of his mental disability, Curley's Wife is an outcast on the ranch simply because she is a female.  She has no one to talk to and nobody who shares similar interests.  She also has no practical skills for ranch life.

2.  Curley's Wife also remains nameless throughout the entire novellete. Steinbeck gives even Whit, a minor character with few lines, a name. This demonstrates that she is unimportant to the ranch hands and that they do not have a desire to get to know her well enough to know her name.

3.  Quote 1:

When looking for Curley in Chapter 3, Curley's Wife says, "They left all the weak ones here. . . . Think I don't know where they all went? Even Curley.  I know where they all went" (77).

She knows that her husband is in town at a brothel and there is nothing she can do about it.  She also fits into the category of "the weak ones" and recognizes that fact.

4. Quote 2:

She asks Crooks and Candy, "Think I'm gonna stay in that two-by-four house and listen how Curley's gonna lead with his left twict, and then bring in the ol' right cross?" (78)

Even though she wants them to think and wants to convice herself that she would leave Curley if the opportunity afforded itself, she knows that that will not happen.  She is too afraid to leave, and the only characters she say this to are the other weak ones.

5. In Chapter 5, as Curley's Wife talks to Lennie, she discusses her past dream to be a movie star and states that she could have made something of herself (88). However, she at one time felt so powerless over her situation in life that she married Curley, a man she had just met, indicating that even now she does not have the courage to leave and try to "make something of herself.