While taking off at a traffic light on an incline in Laguna Niguel, California, my car rolled back slightly and bumped the person behind me. Am I at fault?

I have a question about an auto accident I had with my car. While taking off at a traffic light in Laguna Niguel, CA, my car rolled back maybe a foot. My car and the car behind me bumped slightly. While checking, I saw that I had no marks on my car. The grill on the other driver's car had a crack. I gave my information to the lady. She did not give me her information, wanting only to cover it without insurance. She now has given me a large repair estimate. Was I at fault or was she following too close and not within a safe range?