First of all, may I ask if your MiL speaks fluent English? I am learning another language (European) and we often structure our sentences very differently to them. I could say something and they could very easily think I was saying almost the opposite - for one thing, they love double negatives - or that I was asking a question when I am not! Or maybe your SO does all the translating?
Now, may I speak as a woman in my 60's, who is becoming more and more forgetful, and also getting more stuck in my ways than I used to be - which I strongly try to fight. I have never had a laundry room (and to be honest I am quite jealous about that 😂), so does it have drying rails as well as a tumble dryer? If it only has a tumbledryer your MiL might be trying to save you the cost of tumble drying, and maybe help the planet a bit too? If like me, until relatively recently, she does not have a tumble dryer at home, or any where to put indoor hanging rails, then she may do what I used to have to do with 2 adults in the house and several children, which was to put the clothes on radiators, and when I had run out of them, I would also use the back of kitchen or dining room chairs!
So to summarise, I think it is probably one of three things, or maybe even a mix of them:
a) She hasn't understood properly.
b) She forgets
c) She does it differently at home, so it is ingrained in her mind, and she probably thinks she is doing you a favour!
If it is the latter, and you do use a tumbledryer, then I am inclined to agree with her - sorry! A slightly untidy house on washdays, versus saving money and helping the planet seems like a good call to me.
When it comes to her shouting across rooms, I don't like it either, but from TV news items I have seen over the years, Asian people do seem to shout quite a lot (I absolutely hate generalising things, so please don't be too hard on me for doing so here), so I think you should just cringe inwardly, and not get your SO to keep telling her off.
I don't think you should expect her to be able to change her culture periodically either, just so that she doesn't embarrass you - if you ever go to China I am sure you will do or say quite a few things thst are awkward or embarrassing for her, but she would probably be too polite to mention them.
Now, when it comes to adding salt to the cooking, that is a matter of safety, which overrides any cultural or politeness issues in my mind, although obviously the demand for no salt must be done as politely as possible. If your MiL can't stick to that one, then she must not cook for the children - presuming they are not teenagers, who will almost certainly get themselves far too many salty snacks, for her occasional meals to do too much extra harm!
I presume nobody on here can actually answer your question OP, but I do think that you need to be much more grateful to your MiL, by which I mean, 'relax', stop worrying so much about having a spotless and completely tidy house, a happy and relaxed household is much more important, and I truly believe that once you can let this go, not only will your MiLfeel much more welcome, and your SO and children feel more relaxed and happy, but you will learn to feel more relaxed and happy too.