When she  had this problem before, was she blowing coat then?  Is she spayed?  How old is she? 

Some dogs get  very itchy and allergic when they blow coat.  Some female dogs have a lot more allergic like behavior when they are intact. 

Some dogs do, indeed, have an over growth of skin bacteria and this is because the dog's immune system is not working as it is supposed to.  All dogs have natural bacteria on their skin and at some point the dog's immune system makes peace with the resident, naturally existing bacteria.  Some dogs have a faulty immune system and cannot make peace with the bacteria. 

Other dogs have a faulty immune system and exhibit allergies.  Usually they are allergic to many things and all those things together put the dog over the edge and the dog exhibits symptoms.  Often, changing the food will lower one threshold enough that the dog is under threshold for all the allergens and will stop itching.  This leads people to think "oh is was the food."  It WAS the food but that was only part of the equation. 

I have an itchy dog and she has improved with spaying.  I bathe her 2X a month with Zymox (R) shampoo and then I rinse her with Zymox (R) medicated rinse.  This has helped as well.  I also have been feeding Avoderm Trout and Pea (not really seeing any result over TOTW Pacific Salmon other than a larger emptying of my wallet and I am not dealing with Diamond Foods).  I add 2 TBSP's of Safflower oil (Omega 6 and vitamin E source) to her food, a quarter c. of low fat plain yogurt and some canned mackeral (not a lot) and a single fish oil capsule.  The "5  minute veterinary consult" suggests Omega 6 (dogs make their own Omega 3) as it has shown some ability to block immune response to allegens. 

I feed her 1X a day.  Honestly?  I am not sure any of this is helping.. but her new coat looks like a million bucks and she sure does LOVE her dog food!  She still itches.. just not as badly.. until the next coat blowing episode.