My Annie had a horrible case of demadex when we got her. When the so-called breeder found out she had it and couldn't breed her she dropped her off at a shelter and was pulled by a rescue group. She was about 6 or 8 months old at the time.
She was so sick from the accompanying infections the vet didn't think she would make it, but she did.
She was also on a low doseage of ivermectin for months. Most importantly, it is not considered "cured" until you get at least two clean scrapings. And, then you have to pray they are scraping the right areas.
I am praying for your baby as it is a miserable thing to deal with. Annie scratched herself bloody raw and bald in one day while I was at work and she was in her pen. We had to keep her with little flannel booties on and a turtle neck sweater that we kept pulled up to her ears. And, she was zonked out on benadryl for most of that time.
Now we worry about the long term effects of the ivermectin. She goes to a homeopathic vet and is on a very limited vaccination schedule so we aren't introducing more toxins into her already overly taxed body.
I would seriously look into what Lady's mom has suggested as she has done wonders with Lady and keeping her healthy.