Why does Curley's wife tell Lennie about "the letter" and what does the letter symbolize in "Of Mice and Men"?

Curley's wife tells Lennie that she once met a guy in the movie industry.  She went to a dance with him, and "he says he was gonna put me in the movies...says I was a natural".  This man said he would write to her about it "soon's he got back to Hollywood", but the promised letter never came.  Curley's wife suspects that her "ol' lady stole it", but her mother denied doing any such thing.  Curley's wife still lives with the regret brought on by the letter that never came - she says wistfully, "coulda been in the movies, an' had nice clothes...an' I coulda sat in them big hotels, an' had pitchers took of me...because this guy says I was a natural".

The letter is a symbol of a dream denied.  When she realized that the correspondence was never going to come, and that the life she wished for was never going to happen, Curley's wife married Curley, even though she "don' like Curley...he ain't a nice fella" (Chapter 5).