And I agree you should get legal advice, however be careful, lawyers are usually sharks too the world over, try and find a recommended one connected to school or family. Although I feel sympathy for the lass as I said, because every one of us does such things at some time or another, ( in a hurry to get to work, to meet lover, scared of losing job, kids at the babysitters, another route dangerous etc.) - the circumstances suggest you were not to blame at all of course. Might be time for your GF to get her whiplash and shock treated and her distress noted and a counter-claim prepared. Then it is one citizen against another and might just stop at that and turn it to one side from you. But you never know either - if the sharks keep out of it, the lass and her family may even be decent appreciative folk if you tell them firmly you are not going to be taken for a ride (excuse the pun).