What Causes Non Itchy, Red And Raised Body Wide Rash?

My wife has developed a non itchy, red, raised, body wide rash over the last week. It seemed to start with one large, bite/spot like mark on the underside of her upper arm. Her first visit was a a scabies diagnosis, which annoyed me as it is non-itchy and the rest of the family do not have any symptoms. Her second visit she was given moisturising cream and antihistamine, which she has taken for two days without result. She works as a beauty therapist and and has regular close contact with her customers. She is worried and upset, please could someone offer some advice?