I think (am not sure, though) that the vast majority of (fatal/serious) motorcycle crashes involve single riders, so this is awful bad luck. I don't want to speculate, but I imagine it would most probably have been the impact of how far she was thrown rather than the actual crash itself. Very sad.
Here's a fatal crash in which the victim was thrown off a motorbike while riding pillion.
http://www.standard.co.uk/news/london/pictured-manager-of-chelsea-hair-salon-killed-riding-pillion-on-motorbike-a3476741.html
I think (am not sure, though) that the vast majority of (fatal/serious) motorcycle crashes involve single riders, so this is awful bad luck. I don't want to speculate, but I imagine it would most probably have been the impact of how far she was thrown rather than the actual crash itself. Very sad.