Vet just called! Willow has actually gone from stage 4 to stage 3, which the vet was surprised--but glad--about because that usually doesn't happen. Creatinine level is still higher than it should be but that's also dropped from 6.1 to 4.8, and in the two months since she was diagnosed, she has not lost anymore weight. The prescription food must be helping. Canned food is prescription but I'm still mixing the dry food as half regular and half prescription. I feel much better about having to leave her for a few days.