Can diet soda cause lupus?

According to the Lupus Foundation of America, it is believed that diet is not a contributing factor, I would assume that includes what you eat and drink. But, I did go to church a few years ago with a woman who had all the symptoms of Lupus, and was diagnosed and treated for Lupus, but when she went to another doctor for a second opinion he had her journal her intake of food and drink, and then had her cut out diet sodas (she drank 6 to 12 cans a day), her symptoms disappeared and last time I saw her had not returned. The doctor had explained that a build up of the artificial sweetener used in diet soda can produce symptoms similar to an autoimmune disease; headaches, fatigue, swelling in joints, etc.