Ex Girlfriend problems....please help....?

My ex girlfriend called my girlfriend a , slut, skank and a cksucker the other night at a party in front of abput 150 people and i just found out today. My girlfriend is pretty hurt, especially because my ex had told everyone since before the party that my new gf is a and just wants my dk. I have tried comforting her, but nothing seems to work. What can i do to let her know that she isn't, and she is a better woman than my ex?