how much is it going to cost me to repair a bumper that i crashed into?

i was driving going less then 40 because the traffick was backed up and then, i think the lights turned green ahead because i saw both lanes moving. so the car in front of me started moving then i started and then she slamed on the brakes and i slamed on the brakes but did not come to a stop before hitting her. Iam sure i wasn't going more then 50 when it happened. after checking there was no damage on my car and we could see bearly anything on hers except small lines of paint that came off. She said that she doesn't think that is really damaged but it could be internally damaged and says that i could cot me like 1200$. But i dont think so because there was absolutely no scraches on mine. but the reason she thinks that it might be internallyy damaged is that went we hit, it made a pretty hard impact. well thats because she probably had her foot on the breaks. so i would like to know how much it might cost me, or it is just the paint that came off.
contact me at diakevin@hotmail.com