Answer

There are a few options for this girl at this point... My first step would be to change the diet to a low-allergen diet, such as one based on Salmon, Duck, or Venison (assuming he's never had those ingredients before). If that seems to help (and it could take a few months to know for sure), then this may all be due to food allergies. Prednisone may be needed intermittently until a few months of a strict diet have passed.

If no improvement is seen, I'd recommend trying antihistamines+fatty acid supplementation. Many different antihistamines exist -- both prescription and non.

If no antihistamines work, my next step would be the medication Atopica, which is safer than prednisone but often as effective for controlling allergies.

Your veterinarian should also perform a "tape prep" to look at skin samples in order to rule out yeast growth on the skin, which could require an oral medication such as Ketoconazole. Yeast is very very itchy, and shampoo alone won't eliminate it.
Also, a course of Revolution might be helpful just to rule out Sarcoptic Mange, which can be very itchy and will not respond to antibiotics and steroids.