Why does Curley's wife come to visit? Explain why she starts a fight with the two men.

In Of Mice and Men, Curley's wife
visits and starts a fight for a couple of reasons, one obvious and one
psychological.

Obvious reason:
Steinbeck wants her to. She's a character, a minor
character at that.  She doesn't even have a name.  She's the only female character in
the novella.  She's an archetype: a temptress.  Temptresses tempt.  They tempt men.
 What else is she going to do?  Sing and dance?  She's got to visit the bunkhouse, the
barn, the stable.  She's got to start a fight.  These men are animals, and she's just
the thing to get their blood boiling.  Even when she's not there, she's there starting a
fight.

Psychological reason: she's lonely.
She wants attention from Curley, but he's not giving it to her.  So, she
seeks it from the others.  There's two new guys, one big and one small, and she's
curious.  Maybe she wants to make Curley jealous by seeing her talk to the big buy
because she knows Curley hates big guys.  But that might get her beat up, so I don't
think she would want that.  So maybe she wants to see Curley beat up someone
else.