^^^ Absolutely!! My husband has psoriasis. When I first started testing solutions to start the spray part of my business (HVLP also), I used him as a "tester". The patches of skin will absorb the solution differently than the rest of them. It will be darker - because it's dry, dead skin.
He has been tanning in our base bed - only about 8 minutes at a time - about 3 times a week. It is awesome what a difference that makes!!!
Suggest UV tanning to her. She can ask her derm - he shouldn't be able to deny that it would help