I would guess that it is nothing more than a thick scab. If she isn't favoring the leg more than regular soreness would account for, so long as there is no heat and/or swelling at the wound site, she doesn't appear to be in pain when you press on it, and there is no puss, then I would just leave it be. Some wounds scab thicker and harder than others for some reason. If it is not showing any signs of healing in the next month or so, then I might start to worry. Until then, just keep an eye on it.