A car hit my car, from the back. my 10yr old daughter, who was in the backseat, is complaining of a sore head. right at the back of her head. and also one side of her neck is stiff and feels pinched in when she moves her head. what can i do?

Have her seen: This is the classical description for a whiplash injury. It can be as simple as self healing muscle spasm or a complex injury to the spine. A visit to a facility with x-ray capabilities along with a good exam is reasonable. The head rests in a car are meant to stop such injuries but many kids sit/lean too far forward for them to work.