One of the primary rule outs should be food allergy, especially adult onset and older than 6 years old. Plus, ruleout of endocrine based diseases lowering her immunity to simple staph (hypothyroidism).
She needs to be worked up by your vet, and if they have and not reached any conclusion...request referral to a dermatologist.
I would try Z/D dog food and have a thyroid test if it has not been done...while you wait for a possible referral.
Dr.V
Dr. D.A. Vamvakias
Veterinarian