Hi
Welcome to the MedHelp forum!
It may be urticaria which is usually triggered by allergens, such as drugs, foods, insect bites, inhaled substances, in response to sunlight, cold, heat, stress, exercise, or a viral infection. Other common allergens are pollen, mold, dust, pet dander, or cosmetics. Since your girlfriend experiences an itch, just go over these possibilities in your mind. Something may strike you.
Itchy localized rash can be due to allergic dermatitis, eczema, contact dermatitis, shingles, psoriasis, fungal infection like or Tinea corporis. It can also be a staphylococcal skin infection. Another thing to consider is H pylori infection of the gut with rash. In this one has acidity like symptoms along with rash.
Please consult another dermatologist for confirmation.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!