I'll second Smile by Lily Allen - ska/reggae tempo, good summer song about taking a breakup hard, getting help from her friends and smiling when her ex is crying. Song is kind of new too.
If she is reeaaaallllly scorned, how about Women's Prison by Loretta Lynn.
"I caught my darlin cheatin thats when I shot him down
I caught him in a honky-tonk with a girl I used to know"
My Happy Ending by Avril Lavigne.