Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice.
Since your wife has already been seen by many Doctors including a
Dermatologist, you would have been told about the possible diagnosis.
Blister like rash can occur in various skin diseases and disorders. Post the clear and focused photos for me to have on-the-spot diagnosis.
Well the most probable causes are:
Allergic rash mostly to something from external source, can be
contact dermatitis to synthetic clothes, linen and so on.
Rash due to chemicals in soaps and such things that she might be using.
Hence I would advise her the following in such a situation:
Stop allying anything locally. No soaps also.
Use pure cotton loose clothes.
Take an antihistamine and steroid if required.
Take
Vitamin A and D in therapeutic dosages as per the blood reports, multivitamins with mineral as these are important for integrity of normal skin.
If this and the medications doe not help, it is better to request your Dermatologist to have a biopsy of the lesion to get an exact diagnosis and have proper management.
Hope I have answered your query.
Let me know if I can assist you further.