Was she not holding on to something... Anything? I agree, both parties are responsible for her injuries. As the driver, he is responsible for her safety. I go over safety with any new passengers. If I don't like their attire, they don't climb on behind me. Period. I also give them the chance to make an informed decision: I will do all that I can, to ensure their safety, but riding motorcycle is dangerous -- if they agree to ride, they agree to accept the risks, including death. Not being a jerk, just being honest with them.
My best friend's daughter, 16, wants a ride on my 750, as she thinks it is much 'cooler' than her Dad's Gold Wing. I have a hard time with this, but he says it's alright. Not a gender/age issue (she's like a daughter to me), just a safety issue. Last year, I called her to offer that ride. She was gone, so I ended up giving my youngest son, 22, a ride instead. The rear tube blew out, and we low-sided at 40 MPH, on a county highway. He suffered road rash on his one thigh, and hand, but not bad. He had on a modular helmet, and an armored jacket. It would have been much worse if he had not had any gear (of course, I would not have let him climb on, if that had been the case). Every ride is a risk. Every passenger has to assume that risk. I normally do not give rides, anymore, because of the risks, and liabilities. I do, however, tour, two-up, with my wife, all over. But that is another story. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII