To get a teensy bit annoyed at visiting relative’s ever changing dietary restrictions?

Is it something like acid reflux that she has? Those are the sorts of things you shouldn’t have with if you suffer from that - anything really acidic or spicy, and avoid tomatoes - but you could have a bit. So not an allergy but a medical condition.

Does she drink coffee? Coffee is about the worst thing for it.

Must be a pain to cater for her for you though.

I quite like baked potatoes and don't find them bland when filled with cheese.

I have a SIL like this, she has a new dietary restriction (not GP diagnosed) every time she visits, drives me bonkers. Can't eat gluten but somehow manages to pack away non-GF toast, pasta, crisps. Part way through a 2-week visit she announced she was dairy intolerant but somehow is absolutely fine when it comes to cakes and biscuits. Last time we ate out she ordered Thai green curry and then refused to eat it and made a fuss despite us and the waiter telling her it was dairy and gluten free. So now she gets a plain sauceless version of whatever meat or fish we're having, steamed veg, salad. Or is invited to cook for herself.

Are you sure about the testing thing op?

I was very accommodating to my mil when I was newly married, went to great lengths to assure her comfort, and we were on cordial terms, but every time they came to stay I realised she made a fuss about bedding.

She either didn’t have enough pillows or she needed something to raise her feet up or an extra blanket despite providing extra blankets and pillows etc. It got to the point where I was stressing in John Lewis bedding dept and buying new comforters and triangular pillows and god knows what every time she stayed.

Anyway, it turned out that she was finding the transition to being matriarch in her own family and ruling the roost, to being a guest and having to fit in with another household’s rules, a tad difficult, and this bedding protest as we called it, was the one way she had of asserting her authority.

So I would address this politely but head on op and say to your mil that you took a lot of time and care to accommodate her dietary needs because you want her to feel welcome but, playing dumb, you are now confused because it turns out they are preferences? Could she please explain? Look her in the eye and leave the question hanging.

And if she would like to, maybe invite her to cook while you and your dh go out for the day, so that she feels she has some autonomy in your home? Or invite her to cook along with you?

Either way, I learned that my mil respected me more when I stood up to her slightly, found my back bone, and created some polite boundaries, rather than being too people pleasing all of the time. It shouldn’t be necessary but we actually got on better when I did this as we both knew where one another stood.

I get that we all have different tastes but I genuinely wouldn't find that restrictive at all. Garlic and dill salmon steaks with new potatoes and asparagus, mushroom and leek mac n cheese, spinach and ricotta cannelloni, chicken sausages potato wedges and salad, lamb skewers with roast Mediterranean vegetables and rice, chicken and butterbean stew ... the list is endless! Again I get that we all have different tastes but I suspect you're irritated on principle. Not because you truly can't think of anything to cook.

I'd make a few stand by 'safe' dishes that you can freeze (risotto, lasagne with veg instead of tomatoes in the sauce, mild sauces for curry type dishes etc) and then cook your normal family dinners (avoiding any that are mega spicy) and say to her " I've made xxx tonight, it has a squeeze of lemon juice/ tomatoe puree/ whatever in it, would you like to try that or I have made some <safe bland option> if you would prefer to eat that?" and then ask the next day how it was if she was OK or needs an alternative next time.

I was vegetarian for years, I mostly still only eat vegetarian but I will eat certain things like roast beef or chicken depending on what it's in. After being veggie for so long it messes with your head.

Yep, get her to look through your recipe books and pick stuff she likes. Or get DH to take her out to eat somewhere while you stay at home and get very drunk.

Having read your updates (your prowess in the kitchen sounds amazing and very impressive, btw) I think that your guest (as we're not making it a MiL thread) is taking the micky. Complaining about your plain beans? Nope. How rude. Honestly, I can't begin to imagine complaining about any aspect of food cooked for me while visiting someone else's house! Char it, serve it cold, tip the whole saltcellar in it ‐all you'll get from me is a heartfelt thank you, because you did a nice thing, acting on your good intention to provide nourishment.
There was a thread recently about someone visiting a friend and was disappointed to be served strawberries and cream for desert; to me, this is the epitome of pretty much everything that is wrong with some people.

It sounds like you are going out of your way to be a kind and caring host, and your guest should count herself lucky.

You reverse it.
Instead of asking what they can't eat, you ask them to send a list of ingredients and recipes that they can.

The tomato thing is strange because it looks as though she does eat them after all! But it’s always struck me that tomatoes aren’t native to India and I have wondered what food was like in that area before they arrived. I’ve just googled “Indian food without tomatoes” and a lot of regional dishes come up. I’d be very interested to know what she says if you say straight out that you’re confused because you thought she couldn’t eat x,y and z? I have huge problems with a lot of chilli but I can cope with small amounts, though my stomach complains if I eat several meals with a little in. That’s difficult to explain. Onions and garlic, again, I prefer to avoid and the intolerance is getting worse as I get older, but I can manage a little, occasionally, to be polite. Again, it’s not easy to explain that

Would relishes be an option. Cook mains bland and have dishes of relishes so you can enjoy the flavours still.

Not RTFT but have periodically hosted my DSis whose health issues have regularly required experimental exclusions of certain foods.

I have found that flipping it around and asking for specific dishes (not just ingredients) a person can eat, as opposed to what they can't eat under the current restrictions, eradicates the need for extensive planning (and worrying about getting it wrong!).

Can you just chop up ingredients for what you would normally make and not add the spices etc. to her portion? This is what I used to do for DS when he was younger.

But based on your first response to OPs post you said you didn’t think it was very restrictive and a potato was your first solution what other things would you dish up for a weeks stay minus those ingredients?

I have a family member who used to make up dietary restrictions for herself or her kids - but not actually communicate them until she arrived for Christmas and announced that they couldn't eat any of it. The first time it happened, we spent ages in the kitchen trying to cook new food with the few pans/dishes left unused, only for her to tuck into a load of sweets and chocolate that contained two of the main things she'd said they couldn't eat. The following year, we'd learned our lesson after multiple instances of her claiming she couldn't eat somewhere we'd arranged to meet, or sulking because her parents hadn't anticipated the complete change of dietary requirements in advance of a visit. No new food was cooked - she was just waved in the direction of the kitchen and told to rummage. Miraculously, she managed to eat the entire dinner after all. They now all eat entirely normally, but she tries to control everyone through other means - timings, arrangements etc. Most family members have entirely disengaged.

It's probably that she can't eat these things regularly maybe she's trying yo be helpful at the end of her visit seeing how bored you must be of the food? Or she doesn't mind if she gets the shits at your house now she's settled in a bit?

No, you are wrong. Disordered eating includes those with a specific diagnosis (who may exhibit disordered eating more often), and those without, but it is not minor quirks related to puddings. Example link for definitions - https://www.eatright.org/health/health-conditions/eating-disorders/what-is-disordered-eating.

If you genuinely felt that a friend was struggling, then you would be concerned instead of stroppy about how some food choices inconvenienced you. It isn't a laughing matter.

If you cook mainly Indian food normally and she has said she is ok with a bit of tomato I would get to the bottom of that. So much Indian food has a tomato base. Maybe she just worries about being served tomato in its recognisable form which is very common with fussy eaters.

I feel for you. Making all these efforts for nothing. Are you sure she didn't "test" you, like wanted to be difficult do that she could whine about how you did not accomodate her needs afterwards? If that was the case 1-0 to you OP:).
The polite thing to do when you are invited is to make as little of a fuss as possible: only cite allergies (confirmed) or dietary requests that you always stick to (vegan/vegetarian/religious). I have hosted a boy with Arfid who only ate pasta with nothing on, like no butter/sauce/olive oil. His mum said it's hard for him to be invited somewhere becaause of this. I told her I'd never had an easier guest to accomodate🤣

Disordered eating is specifically a term used to exclude eating disorders but includes strange behaviour around eating ie. Saying you are gluten/ dairy intolerant to avoid ordering a pudding but then eating those things in your own home

@ThatOneUncomfortableEyelash I agree with you, wouldn't stay with someone who felt that inconvenienced by imo not restrictive dietary requirements.

The baked potatoes was slightly sarcastic in that OPs description of what she couldn't cook was OTT. Very much siding with MIL on this one. Even more so with further updates that MIL has favourite food OP cooks so this is a completely non issue for a couple of weeks when she could have just cooked things she knew she'd eat.