There is NO WAY Adam hit her, lets review shall we?
1. When Adam was on the road, Delia was alive but her back was to his car at the time he swerved to avoid hitting the dog. The autopospy revealed she died from signifciant head, chest and neck trauma that would imply who ever smoked her out did it from the front and not from the behind, she was facing behind Adam, so that rules him out
2. Delia wasn't that little, she came up to Vikki's shoulders, putting her at 4-4.5 feet again thats big enough that when she hit the car she'd go UP and smash the windshield then fly over and land on the road or bushes. There would be a significant crack/smash to the windshield of the car, there would be blood on the car and the road, sorry if its graphic buts true. Adam just suffered a chip to his headlight, it looked more like he hit a small branch then anything else, the scarf being under his car is easily to explain it got knocked OFF Delia and the wind blew it up under his car.
3. Adam was driving after 8pm, the time said 8:05pm and when Delia was hit it was 8:00pm, meaning Adam came along 5 mins afterwards not to mention he saw ambulances racing to the scene.
What I find interesting is who was that mystery figure watching Adam in the parking lot? Who is he/she and do they tie into this s/l?