Poor College Kid Needs HELP!!

I hit the back of an 80-yr-old woman's car; her son was driving the vehicle
at the time. We were in some pretty heavy stop-and-go traffic, when he
slammed on his brakes because he admittedly almost missed his road to turn.
He almost caused another women to go in the ditch behind me. There seemed to be very little damage to either vehicle, so we did not report the accident to the police. We only exchanged phone numbers. The elderly woman has been the one contacting me and is not being very kind about the situation; although, her son took most of the responsibility. She claims to have to replace the bumper because of a crack. She wants me to pay the full cost of $701 for this. I am a full-time college student, and cannot afford to pay her and don't know if I am liable anyways. What should I do? I would love some help. Thanks!!

[randalljd]

usually if you hit the back you are liable. but ask to have the damage inspected--she may be exaggerating the damage