How traumatic that must have been for her to fall from a truck but I'm so glad you stopped to save her and that she won't be slaughtered.
I once saved a duck that I used to drive by every day on my way to work. It was all alone (no other ducks) and had an injured wing. The house was a wreck and the yard was full of junk and old cars. I kept hoping that the people who owned him would get him some help but week after week nothing changed. This duck spent all it's time sitting next to one of the tires on a beat up old truck. I found out later when I finally approached them about the duck that they thought he (Fred) did that because he had become 'friends' with his reflection in the hubcap of the wheel because he was lonely. That broke my heart. I loaded up a small dog crate into my truck and drove up their driveway and told them that I had a friend who was 'looking' for a male duck to keep his female duck company and that he would pay 50.00 if they would be 'willing' to part with Fred. They didn't even blink an eye and helped me load him into the carrier. I didn't actually have a friend who was looking for a duck but I had lined up a person who was willing to take him that already had an assortment of ducks and geese that he had rescued. These ducks and geese have a good life with him and their own pond to swim in etc.. I checked in on Fred a few weeks later and he had his very own harem of female ducks and was one happy guy! They had also addressed the injury to his wing and he was on the mend.
Have you named your chicken yet? Maybe you could name her 'Road-a' because of where you found her.