My father, when he was in his 60's had open heart surgery. We were amazed when his extreme case of psoriasis, which covered most of his body, completely disappeared after this surgery. I think it was because of the blood transfusions they had to give him. Considering the intensity of his condition, and the fact that he had psoriasis everywhere--under his nails, in his ears, etc., it was a major surprise when her remained psoriasis free for over a month.
I did notice that he did not have any outbreaks where there were a lot of sweat glands, like under the arm. He had an ultra-violet box that he used every day for years but it didn't help much---made his skin dark and leathery. Also, I did read at a psoriasis site that diet can play a role. I think they said red meat and alcohol could aggravate the condition. I never heard anything about candida having a connection to psoriasis but it could.
Anyway, I think the blood transfusion thing should be investigated. And I do hope your family member finds relief.