I hope you're wrong. She is in no way responsible for the details of the boyfriend's reckless behavior, even if she knew he was reckless. I hope the guy driving the truck pays as much as he deserves to be fined, which is a lot, but I don't think she has any more direct responsibility than the phone manufacturer and the wireless service provider.
I do not have a cell phone.
My question is this. Are text messages saved by the cell phone provider?
The girl friend SHOULD be held responsible. In some small way. If it is proven that she knew he was driving and she contributed to his reckless and dangerous behavior, then she is an accessory.
Much in the same way a bar is responsible for plying some idiot full of alcohol and then letting him drive home at closing time only to crash into some innocent victim.