I don't know if anyone commented on the mail to gf sent to your house or not. What you should do is write in large letters 'NOT AT THIS ADDRESS' and circle her name and put it back in your mailbox. Then the post office will return it to the sender, plus they will change their records to show her name is not your address. Future mail to her at that address will be returned to sender and eventually the gf will wonder where her mail is and find out she can't use your address.
