I mentioned skin mets because it seemed irresponsible not to consider them as a possibility given your sister's history, and I wasn't sure from the question exactly where the rash was.  I have never heard of skin mets being all over the entire body, and if a dermatologist has looked at it, I doubt that he or she would have overlooked that possibility.  Skin mets are not skin cancer, but are breast cancer that has spread to the skin.  There may be other kinds of cancer that can also metastasize to the skin, but I just know about breast cancer.  I do know that it is difficult to impossible to diagnose any kind of rash for sure by looking at pictures.  I thought I had skin mets once after looking at some pictures, and it turned out that I had shingles. I can understand your sister's wish to avoid needless doctor's visits; however, this sounds like a problem that will need personal attention from a doctor.  Has a sample of the skin ever been looked at  under the microscope to get a more accurate picture of exactly what is causing the eczema?