My dog doesn't want to walk and is dragging and scooting her butt and licking her vulva?

When she does walk it is a run then she drops fast and drags her butt.I just took her to the vet today and they expressed her anal glands. The Vet said they were not that bad. She thought she might have been hit by a car. Her vulva looks swollen tonight. Would being hit by a car cause her vulva to swell? She is uncomfortable and doesn't want to get up. She has had a bowel movement but I have not seen her have a urinary movement.