Ultraviolet radiation, both UVA and UVB, has been shown to trigger lupus skin exacerbation and in some cases systemic flares. I contacted one of the makers of SAD phototherapy lamps, Northern Lights. As always, caveat emptor. Her rheumatologist is considering aphoresis because 7 months of cytoxan treatments have not shown adequate progress. From your question your daughter must have severe, active nephritis that is not improving.
Apheresis has a controversial history.
In comparing treatment among patients with severe lupus nephritis who were randomized into two groups, one consisting of treatment with pulse cyclophosphamide and prednisone versus a second group of patients treated with pulse cyclophosphamide, prednisone and plasmapheresis, no difference in clinical outcome was noted. Your daughter would fall in the latter group for consideration of plasmapheresis. The risk of complications of plasmapheresis versus continuing renal damage from active lupus nephritis which can cause renal failure are the factors that her doctor is using to make the recommendation for apheresis. Her physician has more facts than were included in your question. The recommendation appears to merit careful consideration and is consistent with sound clinical practice.