I do feel sympathy for Curley's wife. She is a very young woman—a teenage girl—and the only woman on the ranch. She feels isolated, and she says the following to Crooks, who tries to shoo her away when she visits for fear Curley will be jealous:
Think I don’t like to talk to somebody ever’ once in a while? Think I like to stick in that house alla time?”
She is dissatisfied with Curley, a man she married because of a lack of alternatives. He bores her with all his talk about the fights he has been in and his blow-by-blow descriptions of them. She tells Lennie she is glad he roughed Curley up and says she would like to do the same sometimes:
I’m glad you bust up Curley a little bit. He got it comin’ to him. Sometimes I’d like to bust him myself.
Curley's wife feels she could have been in the movies, a story she keeps going back to. She says:
An’ a guy tol’ me he could put me in pitchers.
Curley's wife insults the ranch hands by calling them bindle stiffs and threatens Crooks with lynching, but it is clear she is lonely, bored, and unhappy in her marriage to a jealous and self-centered man. When she talks to and flirts with Lennie out of boredom by having him touch her hair, she does not appreciate the danger of her actions.
Like the ranch hands, Curley's wife is trapped by circumstances. Her attempts to reach out, however misguided, lead to her death. It is hard not to feel sympathy for her given how lonely she felt on the ranch and because she died so young.