On tonight's commute I happen onto a roadie type in an all black outfit, and only equipped with a headlight. I decided to follow him at a safe distance for as long as he was going in the same direction, covering his back since I had reflective outerwear and rear reflectors and flashers. After following him for a mile, out of nowhere, there was a sudden blur of a bicyclist passing by us (in the traffic lane) going against traffic in dark clothing and no lights, then just as suddenly there was a blowing of a car horn followed by a crashing sound. I looked back to see in the headlights of a stopped car, a bicycle and rider on the ground, I and the other rider turned back to help, and discovering that it was a young woman who was also on her way home. Luckily for her, she only sustained a bruised knee from the crash, and she only had a short distance left to get home. After she declined any help from us, and after observing that she did not exhibit any major injuries, the other rider and I continued on our way, but after we advised her that she should make herself more visible when riding at night, and that I consider riding with traffic much safer than against.