I'm by no means an expert, but could the dewormer have been contributing to the diarrhea? Certainly four days is not long, so as you noted anxiety is also probably a factor as well. I'd be more inclined to give it another couple of days to see if things firm up now that she's finished the dewormer. Switching foods probably won't hurt, but I think there are other variables you might rule out first.
Another couple of thoughts: are you feeding her 2x a day? 3.5 cups in the morning seems like a lot at one time to me. For comparison, my girl (61 lbs) gets about 2.5 cups a day, split between morning and evening. (She eats Blue Buffalo, which is higher protein and thus she doesn't need a lot.) If she's being fed once a day, I'd try splitting her food up into two meals. Adding a bit of warm water (not so much that it's soupy, but more of a thick, gravy-like consistency) helped Sweep with choking/bolting food.