@PurpleOkapi
Again, the OP didn't say her GD has public 'screaming meltdowns', she said she was quiet. And it seems to have escaped you that, yes, making these sort of assumptions about someone on the basis of their disability is prejudiced and discriminatory. Substitute the word 'race' or 'sex' for 'disability in the previous sentence and see does that make it more obvious for you. In your mind autism = screaming meltdowns and disruptive, anti-social behaviour that the bride has wisely banned from her wedding. In previous posts you have likened the exclusion of the 11-year-old to excluding a badly behaved ex, or an alcoholic who passes out on the dance floor!! Can you really not see how disablist you're being? It's shocking!
And the thing is, the OP never suggested the exclusion had anything to do with the autism diagnosis, but rather that the bride and groom had decided on a child-free wedding. So I ask again - why are you inventing this narrative?
The uncaring, unsupportive parents are another pure fabrication on your part! One error in mentioning the wedding to their child and you are painting a picture of incompetent or apathetic parenting.
But this child won't be getting that support
And there has been no suggestion that the OP's daughter actually asked her mother to miss the wedding, something you're presenting as fact, when the OP has given no such information.
Then when that didn't work out as planned, they asked the bride's grandparents to miss their own granddaughter's wedding
I suggest you stop inventing backstories and motivations and if you want to advise the OP, stick to the facts you are given or to insights borne by experience. The way you're posting about autism is really ignorant. I asked if you had experience of the condition upthread and you replied you had lots, but I really can't believe this to be true any more.