I think you need to see a veterinary dermatologist instead of your regular vet.
This site may help you find one
http://www.acvd.org/site/view/55607_FindADermatologistAlphabetical.pml
This might be due to thyroid problems triggering an allergy to a food item or something being inhaled.
You can see if plain Benadryl will help with the itching. The minimal dose is 1mg per pound of dog so a 50 pound dog would get two 25mg tablets every 8-12 hours.
Sebaceous Adenitis (SA) is a hereditary skin disease often leading to progressive loss of hair which is found in Standard Poodles. That is another possibility. You can read about this disease here
http://www.poodleclubofamerica.org/healthsa.htm
She is within the range of age when it can show up and its one of the sorts of problems that makes me suggest seeing a veterinary dermatologist.
Hope this helps you!
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