My girlfriend also has severe diet restrictions. She cannot eat any sulfites, grains or potatoes, (all nightshades have solanine). But she can eat the following three veggies, Yuca (taro), name'(Pronounced nyAH-may), and malanga (coco). Imported from from Central and South America.
One caveat. They need to be boiled before eating. The yuca needs to have the cyanide boiled out of it. The name' and malanga need to be boiled with baking soda to leach out the oxalates. That is what the natives in Africa do where those vegetables originated and are still important staples in their diet.
My girlfriend has suffered severe migraines since she was 12 years old but her 23andme DNA analysis pointed to MTHFR defects that can be mitigated by avoiding certain foods including sulfites. More or less free from headaches now. So these are the food options instead of potatoes:
www.melissas.com/Name-Root-p/1395.htmwww.jctropicals.us/products/malanga-cocofood52.com/blog/12433-all-about
-yuca-and-how-to-put-it-to-good-use