Dog scared of car after accident?

My very active 30 month old Labrador Is now scared of travelling in any car. In Nov/Dec last year I went to Oz for 3 weeks with my mrs, and left Doris (the dog in question) with the in-laws. She is familiar with them and has no trouble staying away from us occaisionally. Whilst with the in-laws they had a minor car accident. A youngster driving too fast rammed the rear end of the car with sufficient force to knock their hats off and write his own car off. Doris was flung around in the car a bit but not injured. Now she acts terrified in the back of my car. I am very active and Doris comes everywhere with me. I run in the woods, go for long walks etc and all this usually involves an initial 5-30 min (approx) car journey. Doris will spread herself across the back seat and shiver uncontrollably, sometimes even too scared to take a treat, which is previously unheard of. Before the accident she would be sat in the middle of the back seat watching the road in front for rabbits and pheasants, or sticking her head out of the window with her ears flapping around in the wind. Sometimes when we have been for our walk and its time to go home, she will casually walk away from the car when i open the door, although she will eventually get in without being forced. I have never had to force her in against her will. I have tried reassuring her with small treats whilst on journeys but to no avail, sometimes she wont even take them, and she`ll just lay across the back seat all tensed up, shivering and always looking away from me. She does seem to have become a little nervous in herself, sometimes refusing to leave the house, but always back to her normal hypo self when she eventually gets out and about. It breaks my heart to see her terrified in the car but I dont know what I can do, I want my Doris back!!