Stereotypical comments include:
'You don't need him anyway! You're a strong independent woman and don't need a boy in your life!'
'He's most likely gay - why else wouldn't he want you?!'
'He's a dick, he's obviously attracted to you but too immature for a relationship.'
etc. You're her friend, you should know how to cheer her up. My friend got rejected a while back, so I turned up at hers with a few bottles of wine and junk food. Use your imagination.