I NEED HELP ASAP!!!!!!!!?

A few days ago me and my girlfriend were driving over this bridge near my house and when we got on the bridge my girlfriend accidentally bumped into the back of another woman's car when we pulled back there was no noticeable damage to the car but the lady called the police anyways. Once the police officer got there he noticed there was no damage to the bumper either and told my girlfriend that if she would take it to court he would testify for her. Today we just gotta call from the lady and she wants $610 to buff out the scratch or $780 to replace the whole bumper (keep in mind this car is brand new) but the problem with this is my girlfriend is only 17 and she works at the mall, there is no way she could pay it off seeing as though she only makes around $80 to a $100 a week. And the woman wants it payed off in 3 to 5 days... So what should she do? Take it to small claims? Or is there no way out of it?