I'm going to address your last post a chunk at a time, because I'm writing tomes here.
she can’t mask the truth
Her older sister is forever saying sometimes just lie!"
As I type, there is a voice in the back of my head screaming "what right-thinking person wants their child to learn to lie?"
Part of me is genuinely horrified that you want her, or anyone, to do that.
The other part of me recognises that you don't understand why I feel like that, so here goes my view on why autistics struggle with this.
Autistic people tend to interpret rules strictly, will initially prioritise the first rules we learn over later rules, and will then spend a lot of time thinking carefully about what "right" and "wrong" mean in order to resolve apparent conflicts between rules. We prioritise ethically correct behaviour, that is acting according to the rules, more highly than avoiding hurting people's feelings, because:
- what hurts others feelings is hard to understand, I can't read another person's mind, and that person might be lying when they say "you've hurt me" or "no, it's fine",
- no matter what you do, there's a risk of upsetting someone somewhere,
- we understand that sometimes hurting feelings is the right thing to do to avoid greater harm, and
- doing wrong is a form of unkindness to everyone because society only works properly when we all obey the same rules as to basic conduct (hence why we have laws and prisons and courts).
Whether I hurt someone's feelings is an impossible minefield, but what I can do is make sure that I have done my best to do the ethical thing.
All humans are taught from an early age that lying is wrong and we are often punished for lying to our parents and teachers. I strongly suspect that adults teach their children not to lie because it is much easier to manage your children when the child will admit to breaking the china instead of blaming their sibling/the dog/etc. We are told maxims like "the truth will out" to make us fear being found out as a liar and shown the Nolan Principles and Ten Commandments as examples of authoritative rule-setters prioritising honesty. With autistics being perfectionists (e.g. not getting 100% on spelling test makes teacher fear a meltdown) and have a strong sense of shame (e.g. the school must not find out about the meltdowns that happen at home), we really fear being caught in a lie and we really take seriously the rule that lying is wrong. (This is why there is part of me screaming "but why would you want your child to lie, what is wrong with you?") We are then later told "actually, we lied to you about that rule, lying isn't always wrong and in fact sometimes you should lie but the rules of when it isn't or is OK to lie are really complicated and we won't help you figure them out, you are on your own with this". OK, no one actually says that directly in those exact words, but the sister saying "sometimes just lie" is an example of what the later change of message looks like in practice.
As a consequence of all the above, lying, even "white lying", is a huge challenge for many autistics. It's almost impossible for me to tell a direct lie. What I've learnt to do is to skilfully leave details out to spare people's feelings and devised criteria (based on the Rotary four-way test and similar principles of correct speech but also considering how leaving things out to spare feelings in the short-term can backfire in the long-term and cause greater harm) to decide when to omit details.
To give a simple example, if you and I were dress shopping together and you asked my opinion when trying on, I would be completely honest, no omissions, because it would be less kind to let you buy an unflattering dress than to tell you that it looks like a bucket of sick was tipped over you. If you had already bought it and were wearing it on a night out and asked me for what I thought, I would try to find something nice about it, anything, even just "I like the buttons" or "the neckline flatters your bust" or something that I could say truthfully without saying falsely that I like the whole dress or else say I don't like it and ruin your evening. If you showed me the dress at home before going out, I would tell that it was unflattering so that you could change it for something nicer before you went out, again, "friends don't let friends go out looking like a sack of King Edwards" because to do so is unkind.
A more complex and much higher-stakes example, was going to see my grandfather when he was dying. I knew he would ask after his beloved cat that we had taken in and promised that we would care for but not been able to keep because it had attacked one of our other cats and broken her tail. I omitted the detail that we had rehomed it and instead very selectively relayed detailed true information from the new owners about how well the cat had settled in (without saying where the cat had settled in) and how much it came for strokes and cuddles (not saying who it went to for strokes and cuddles) and hoped and hoped and hoped that he wouldn't ask outright whether Tiger was still with us. I had to rehearse in advance the selective truth-telling to make sure I wouldn't slip up, because he had already had his heart broken once when he lost his cat at the start of his end-or-life care and I did not want to break his heart a second time. Even with the stakes so high, I could not bring myself to say "Tiger's doing really well with us", it's like my tongue freezes in my mouth and the words will not come out. Thankfully, he didn't ask where Tiger was. I am confident that, by only telling Grandpa what was true but also would not hurt him, I behaved ethically and kindly.
I strongly suspect that posters will think about writing replies quoting that sentence and saying things like "omg he was a dying man you could get off your fking moral high ground just once and lie to spare his feelings", to which I say that it is not a choice and repeat "it's like my tongue freezes in my mouth and the [untrue] words will not come out". This is one of the reasons why autism is a disability, it is a "mental impairment" causing a "substantial and long-term adverse effect" to the autistic person's "ability to carry out normal day-to-day activities" like telling "white lies" in circumstances that other people wouldn't think twice about.