These things happen, there's nothing you can do. So long as you were driving sensibly, and observing the speed limit, I don't think you should blame yourself. Animals run out into the road all too often, and it's often impossible to stop in time. I've never hit anyone's pet, but I have accidentally hit a couple of things, purely because they did something stupid, like run in front of the car. I know how you feel, it's awful, but try not to beat yourself up about it. These things happen. x