Yes, she should - but I am sure most people will have had a dog get loose.
I wouldn't leave any of mine in the back of the truck, knowing they could get loose easily - not worth the risk.
If they had done damage and been shot, I also wouldn't blame the farmer - it would be my fault for letting my dogs get into that situation. I wouldn't retaliate in anyway, however gutted I was.
On the other hand, if the dogs hadn't done anything, and he shot them anyway - I'd be doing time.