She's been eating cheesy potatoes for 30 years. Some people have problems...
I read somewhere that the potato introduced to Ireland (of Potato Famine fame) was a nutritionally complete potato, in that it had a bunch of vitamins and protein in addition to carbohydrates. I guess there's a whole lot of potato varieties, but the ones that spread around the world were the most stable and consistent. And white.
Yeah, that's some commitment. I've watched the whole episode and basically a bunch of doctors make her touch a tomato while she gags. Progressively she tries other foods and agrees on a more diverse diet. 10 days later she is still sticking to her new diet but still craves the potatoes, problem solved! (If only it were that easy in real life, i always wonder how good they are doing a year down the road)