So recently I took in a female boxer puppy. She's a rescue and was very obviously abused by whoever had her before. I didn't see her parents but I was told they were both boxers. Now about her size and weight, when I got her she was roughly 5 weeks and weighed maybe 6 pounds. She is now about 13 weeks and only weighs 13 pounds. None of her ribs or spine are visible and she has great muscle definition . She's been dewormed twice and will be again for a 3rd time very soon. We also have her on an all natural grain free food. (Sorry for all the sporadic information I'm just writing as I think.) Is she just super petite or should I set up a vet appointment?