$400 ??? That is all she is asking. She did you a favor by not calling the cops. She could have have easily said a much higher amount. This is nothing, you rear ended her , so it was your fault. She did you a favor and could have made it much worse. Do the right thing. Be honest and tell her you do not have the cash immediately but send her what you can and the rest in a couple of weeks. Do it before Karma catches up to you.