As its episodic it may be due to seasonal allergies. It may be a combination of food allergies and seasonal allergies pushing her over the edge.
Purina isn't the best of foods though its OK for a supermarket food. A food like California Natural might work for her or Wellness fish, rabbit, duck, or venison. A friend of mine who raises the breed says lamb bothers her dogs and chicken doesn't.
And see if the kids have given her any treats. Dogs can be allergic to treats too.
And then this might be flea bite allergies.
Bites from flying insects can trigger this sort of rash too.
The breed is prone to allergic reactions.
My suggestion is instead of your regular vet you should see a veterinary dermatologist with her if you can. This site might help you find one
http://www.acvd.org/site/view/55607_FindADermatologistAlphabetical.pml
Allergy testing and knowing what the issue is could make a big difference in how you treat her problems.
Hope this helps you!
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