Accident; No damage, No injury, Left scene?

I was driving lastnight in some heavy traffic in center city Philadelphia. Traffic had stopped and as I was trying to get into a lane to the left of me, the genius in front of me decided to slam her breaks on (due to cellphone usage). I had my foot on the break slowly rolling forward and "lovetapped" the lady in front of me. She got out of her car to inspect the damage (non was visible, there is no paint on my car, nor has there been ANY visible damage, whatsoever). She was very rude and flustered. She came to my window and I agreed to give her my information. She came back with a pen and paper as she was shaking. I was in the middle of giving her my numbers for the vehicle, and she just asked for my phone number to sort this out elsewhere. I agreed, she called me, I said to pull off to the next exit and meet on the shoulder. After hanging up, i proceeded to drive away and pulled off on the closest exit which happened to be on the left side of the expressway. She did not follow, so I went back to my house. Later that night, the police had come knocking on my door, but I didnt answer. What should I be worried about? There was NO vehicle or bodily injury to either me or her.