Curley’s wife is not a villain. She is lonely and frustrated.
The guys consider Curley’s wife “a tart” because she seems flirtatious. Curley is also jealous and always rearing for a fight. George tells Lennie to keep away from Curley’s wife, because if they fight they are going to get fired.
Curley’s wife is always looking around, trying to find her husband. This makes the men nervous.
"Oh!" She put her hands behind her back and leaned against the door frame so that her body was thrown forward. "You're the new fellas that just come, ain't ya?" (ch 2)
Curly’s wife does seem like a flirt. Consider her situation though. She is the only woman on the ranch. Her husband is a jerk. She was once a pretty young thing with dreams. Once she married Curley she succumbed to a no-name existence.
"What kinda harm am I doin' to you? Seems like they ain't none of them cares how I gotta live. I tell you I ain't used to livin' like this. I coulda made somethin' of myself." (ch 5)
She is trying to find her way in the world, and come to terms with her new existence. Sadly, she tries to talk with Crooks and Lennie, and this causes conflict. She is not a villain, but she is the source of the conflict that leads to Curley's hand being broken and her own death.