Um, I hate to say this, but you must be way overfeeding her for her to gain 4 lbs in 1 week, and that alone can cause diarrhea. With all dogs, but especially large and giant breed dogs, it is very important for them to have slow even growth. Fast growth means that their joints are forming too fast and not necessarily well, which means hip and elbow dysplasia. Feed her to keep her athletically lean, no extra weight. Keep her on probiotics until she has had normal stools for at least 2 weeks.
You may want to look into a supplement by the Honest Kitchen called Perfect Form. A lot of rescue dogs have had really bad cases of worms that have damaged the gut lining and it may take months for the damage to heal. Perfect Form has some really nice ingredients to soothe irritated intestines and firm up sloppy stools.
Have you looked at the Large and Giant Breed Puppy Nutrition thread?
