It's a dilema for sure. I would be as strict as you can stand to be. I have found I can tolerate chicken tacos with onion and cilantro only with corn tortillas, soft NOT fried. I can tolerate small portions of corn, once a week or so, some cannot. Also, I have a Chinese restaurant near me that makes a chicken and green been dish with brown rice that I order, hold the sauce (dang, best part).
As for sour cream or any dairy I personally wouldn't touch it. And no way would a mushroom come near my lips, but everyone is different. I find it easier to be strict than to walk a line, kind of like one cookie isn't enough, I want a dozen and Candida will be thrilled to have even a little of the foods it loves.
Each to his own, I generally try to make choices that lead to solving the problem not prolonging it. Good Luck!