Welcome to Justanswer. Your wife has an abscess or even a carbuncle from the description of the disease. This requires active treatment with prescription antibiotics, preferably those with activity against MRSA infection.
The non healing of the abscess may be due to many reasons:
All dermatologists and physicians have experience in treating such infections.
Read more about How to Manage Recurrent Boils: Treatment of Furunculosis.
Hope this helps.
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My answer is for your personal information only. It should not be used as a substitute to visiting your doctor. No treatment should be tried without first consulting a doctor.
Thanks for the detailed description. As these are blisters with fluid, then it could be Bullous impetigo, also of staphylococcal in origin. Anyway, as she is seeing the dermatologist tomorrow, we will know for sure.
All the best!