did your vet check for any kind of worms? when i asked my vet about worms he said the affects are weight loss and them having difficulty gaining. so i'd check into that. oh, but i do hope that she gets better coco is 4lbs and i could just imagine how fragile she is at that weight. pls tell her that coco hopes she feels better soon ruff. ruff.
p.s. pls. keep us posted on her progress.