ORIGINAL: davidmil
I'm guessing shot from above and it just skinned along under the skin after tearing up some back muscle. Second vote would be a whack by a car and skidding across the asphalt to take off some hide.
This is my thought as well, then the animal will loose some hair and weight from infection, and end up looking like she does. Suppose someone hit her with a BIG mechanical BH, that would lay here side open like that, and then she'd take a little time to heal. She certainly may also be weakened enough to feed some "dogs" in your area as well.