I used to think everytime I hit a bump or ran over a cup or something in the road, that I had hit something living. I would drive back, get out of the car,.... Not usually three hours though, maybe just a couple of trips.
Your daughter is probably going to need professional help if she does this a lot (or does more things like this). She is going to have to come to terms with it herself. You cannot convince her. She is going to have to realize it is unrealistic. For example, I still think about this when I hit a big bump or run over some inanimate object that makes a noise or bump - I just think to myself okay wouldn't I know if I hit something like a person (which would be the worst case scenario). I force myself NOT TO GO BACK! I didn't hit a person, I would know if I hit a person - it wouldn't be like running over a big stick or a McDonald's cup. It may still get to me and I usually tell my husband about it who says, you would know if you hit a person. I have even asked him to go back because I have made a pact with myself not to entertain these fantasies that I really know are just that. He will not go back for me. He says he knows I would know if I hit a person and would never have left the scene, and I know that is true.
Hope this helps you to understand. However, as I said, she probably needs counseling. She needs to work this out; you cannot work it out for her. You may be able to help walk her through the reality, but she may not be able to hear it from you. I always felt my mother was being critical and telling me to just stop it (not just this but many various compulsions and obsessions that I allow to run me). The therapist doesn't tell me what to do or think (or not to), but helps me to break it down and make choices for myself.
