Her parents just sat there and said nothing? That’s madness.
I have two autistic children, complete opposites of one another.
My daughter has no filter, can say exactly what she is thinking which of course can result in her being very rude. She is pulled up on it and corrected EVERY TIME. She went through a phase of commenting whenever she saw an extremely overweight person. Never directly to them but she would ask us in her extremely loud voice, ‘MOM, WHY IS THAT MAN (enthusiastic pointing) SO FAT/GINORMOUS/HUGE?’ ‘DAD, LOOK AT THAT FAT WOMAN’. Every time she was told that what she was saying was inappropriate, it hurt the persons feelings and she had to apologise if the person heard her, as we did too.
She went to school with a child who had dwarfism as did both his parents and every time she saw the dad (never the mum or child) she would say, ‘MOM LOOK THERE’S HENRY’S SMALL DAD!’ ‘HENRY’S DAD IS JUST SO LITTLE!’
She can also comment on baldness especially if it’s not the norm to her (such as a bald child) or if someone has a very obvious physical disability, she can comment loudly but it is never to be intentionally nasty, the baldness and disability comments tend to be curious ones just in a very loud voice which again she is corrected for doing so. How else will she learn?
The comments have become less over time (she’s 11 now) and she has become quite good at correcting herself or stopping mid sentence. your dn is 9, she is old enough to be told, it should have been consistently corrected from day 1.
I hate when parents use their child’s ASD as an excuse for everything and opt out of parenting because ‘well they’re autistic’. The children still need to be taught right from wrong, they need consequences, they need praise and yes, it is a thousand times harder parenting an autistic child but it isn’t optional because they have a diagnosis. The right techniques, consistency and a hell of a lot of effort needs to be used.
You didn’t do anything wrong op and your dn’s parents certainly aren’t doing her any favours, I’m sure she’ll learn this lesson the hard way some day. I wouldn’t be complementing her in return though (I understand your thinking that it may alter her train of thought) I’d ask her to stop and then leave if she didn’t and if her parents didn’t intervene.
I get that it may be the easier option to just ‘let it be’ rather than the potential 1hr+ meltdown that may ensue from correcting behaviour or being hit, bitten or kicked, I’ve been there! But sorry, to me, it’s just not optional.