Eczema Treatment Care

My daughter has a really bad rash covering her body. As of now, we do not know the source of it. Initially, the doctors told me that it was contact dermatitis. ( A rash caused by something she touched…or came in contact with) Since taking her back a couple more times, they now say it may be from a virus, or who knows what. When given instructions in the beginning, I was told not to use soap on her skin but twice a week, and to keep Eucerin or Vaseline on her to keep her skin hydrated. But this is when they thought it was contact dermatitis. Her rash is bad as ever. It has been almost 2 weeks. If it isn’t…and I’m almost certain it isn’t, contact dermatitis…could the soap still aggravate the rash? I am thinking that if the rash is being caused by an internal issue, then soap should not make it worse. Am I wrong? BTW, I am only using unscented, sensitive skin soap on her…maybe only once a week now. I will do anything to make her better.