What flash of memory does Christine have while walking back to the car with her husband in Part 2: The Journal of Christine Lucas, November 10?

As Ben and Christine began to walk back to the car they saw fireworks in the sky. Suddenly Christine began to have a memory. Christine saw herself on the roof of a house with a woman she instinctively recognized as her best friend. She and the woman talked about a man with whom the woman wanted to set Christine up.