Gizmo'sMom (what is your name, btw?

) scratching can be due to all those things Jill has mentioned. I think the fact that her tail was so itchy, she bit it means something is definitely bothering her. You've been assured it's not fleas, so I would suspect allergies. Food allergies are pretty "easy" to resolve, though Jill's experience was rough and her dedication to helping poor Tess out has been heroic. Jane has also had to jump through hoops with her Lincoln's allergies.
Many times, you can simply eliminate grains (all wheat, barley, millet....) and eliminate chicken and try a food that has only one or two sources of protein at a time. I often recommend to customers with the same issues you are having, to try Taste of the Wild Smoked Salmon, Acana Grasslands, Natural Balance Duck and Potato, EVO Red Meat or Orijen Red Meat, or 6-Fish - to name a few. Grains cause an awful lot of itching in many dogs, lack of good coat, skin, chronic ear infections, bloating, gas, obsessive licking .... Check the indgts. in treats as well. There is a recent thread in the "Alternative Diets" section on "Healthy Treats" and several links to products that are for dogs prone to allergies.
I'd definitely try wiping Gizmo down every time she comes in from outdoors - it can't hurt. See if she spends time on carpeting and make sure those areas get vacuumed often.
Her immune system may not be the best due to her background, but you can try to figure out what seems to be her triggers and try to eliminate those. I think I'd try to the change diet as it will be much cheaper than an allergy test. As Jill said, stick with it for a little bit as it can take a few weeks or months to see a huge change. Oh.... and please avoid the "hypoallergenic" products/kibble from the vets' ! Those would be from Hills, Pedigree, Royal Canin... I dunno.... so many .... Check them out at
www.dogfoodanalysis.com and see why they are anything BUT hypoallergenic since they are chock full of grains!
