The powerlessness of Curley's wife is in part because she is never named other than by her association/possession by Curley. She is also ignored and condemned by the men on the ranch because they are afraid of Curley. She is powerless to change her position or better it, and listlessly goes from one uncontrollable situation to another, with the presumption that she has control. She left her mother’s house when she married Curley, thinking that it would prove a point to her mother. Since her mother is not present in the text, one can assume that the point, whatever it was, was never proved. She thinks she has control, but does not, which is cemented when Lennie breaks her neck by simply shaking her. She is weak and insubstantial.
As for language in Of Mice and Men, there is a contrast between Steinbeck’s descriptive prose and the vernacular of the men. They speak like men on a ranch would have spoken—roughly and bluntly and without recourse to who might hear them. The language is very realistic.