Oh you poor thing. This same thing happened to me early last year with our 3 month old pup. We were outside and she got out because she wanted to play with us, then she saw a car. Its horrible. I was misserable for weeks, and now when I see a dog out, near a road, I often have a cry. It's such a horrible thing to happen, but we just cant stop it. Hope you feel better soon, just remember the good times with her, it helps.