Well, I spoke to the vet tech at my vet's office about the possibility of switching vet foods before taking her off of it entirely and the conversation did not go well (surprise surprise). My vet believes that taking her off of the vet food will cause all of her problems to come back. She also believes that if I put fish oil or any other type of oil on her food for her itching, even the vet food, that it will cause Sadie's diarrhea to come back. The tech seemed insulted when I suggested that Sadie's skin was dry because the food lacked something. I was insulted that she actually said to let Sadie itch, that since she didn't have any red or raw patches yet that it couldn't be that bad. I don't have raw patches but that doesn't mean that in the winter MY skin doesn't itch and drive me crazy!
I wholly disagree with my vet. Although the vet food definitely helped to cured what ever was wrong with her (despite extensive testing we never found out), I don't believe that Sadie has the 'sensitive digestive system' that the vet thinks she has. I've since started giving Sadie the odd treat, (my neighbor also likes giving her small bits of pepperoni occasionally), as well as a number of healthy people foods, such as fruits and veggies and she's had no problem with digestion. She's even gotten into my parent's sheltie's food and had no ill effects, which does not seem to me to be.
I started putting an Omega 3 oil on her food a week ago as well as gave her a bath and I noticed a difference immediately. Love the Mane and Tail Shampoo and Conditioner, they make her fur white, soft and shiny and since putting the oil on her fur I haven't seen her scratching once. I checked her skin and it no longer looks dry. Even the dry patch where her fur meets her nose is gone.
I'm going to give her a month of the oil on the vet food, just to be safe, before slowly trying to switch her to a holistic food.