Dermodectic mange

I was speaking to a friend whose dog has suffered with demodectic mange inspite of veterinary treatment. They are about to go to a consultant but are not sure if putting the dog to sleep might not be kinder. I asked about the diet and recommended this site as she had tended to dabble with “expensive” kibbles and free flow mince and is not, shall I say, a good listener. On our rescue forum we have an experienced fosterer who kept a jrt who had this and we all worry when there is a flair up. I wonder if there has been any dietary support that has been successfully trialled as these dogs have compromised immune systems so I would shrink from advising raw chicken as salmonella is a consideration, I think.