I have a picky mother rather than a picky child.
She tells me she cannot eat a very wide range of foods, although she has never asked for conventional medical help for her problems. It's all self-diagnosed and treated.
She's also vegetarian. So as far as I can remember it's no meat, fish, very little egg, no soft cheese, no vinegar or citrus/acid fruits, no nuts, pulses or soya products, no spices, no onion, no cabbage. But it's hard to keep track.
I am a decent cook, who can work with allergies or most dietary preferences.. I can do vegan - no problem. I can do gluten free with ease.
When she used to visit me I would try hard to cater for her, but she would always turn round and tell me that something had 'disagreed' with her and then there'd be a post-mortem about what I had done wrong. For example I had made her a trifle, and she'd eaten a large helping. But then she said didn't I know that I shouldn't have put strawberries in because of the oxalic acid.
It was a relief when she stopped visiting me.
I am dreading a forthcoming birthday celebration with her, where I know she will go through the menu at the lovely hotel informing the entire table of all the things she cannot possibly eat...