The best inference that we can make would be that Curley's wife marries Curley either out of spite, out of love, out of other options, or as a result of all of the above possible options.
We know that Curley's has married Curley merely 2 weeks prior to the beginning of the story. We know that Curley is apparently bragging about having married a woman as sultry as his wife, and the farm hands have been feeling the heat of his boastful behavior.
This is because, from what we can gather, Curley's wife acts the part that she has tried to play for many years: The part of a showgirl, or Hollywood starlet which she is quite close to getting shortly before she opts to get married.
From what Curley's wife tells Lennie in their first (and last) conversation, she had met a man who did go to Hollywood (or so he said) and that was supposed to write to her whenever he got there to give her a chance in show-business. However, that letter is never received.
I never got that letter, " she said. "I always thought my of lady stole it. Well, I wasn't gonna stay no place where I couldn't get nowhere or make something of myself, an' where they stole your letters. I ast her if she stole it, too, an' she says no. So I married Curley.
It seems that Curley's wife suffered quite a trauma from this event, for which she later chooses to make the huge mistake of marrying instead, albeit, out of love. It is very clear that she is not in love with Curley. Otherwise she wouldn't be giving Slim "the eye" and she would not be working so hard to get seen and admired by the farm hands.
I think that she married him to get a reputation as she is heart broken of not having the opportunityof being in the movies so what she decides to do is use her femine side to attract attention to herself in a different way. The reason I believe she married Curley is also because he is the boss' son and therefore she could gain more out of Curley that just being a women who isn't really respected in her position in society especially if you were hanging around with migrant workers.