I don't have DC but I'd get this as an issue.
TBH, everyone expecting you to shit miracles and be 100% there for everyone.
Then stopping you putting in reasonable accommodations for DC asd is beyond cfery.
I would feel guilty for years as I have a good dose of ND rejection sensitivity but the whole idea would send me into a massive meltdown and I'd refuse to go or be a bridesmaid as I just would not cope.
I'd then look like the massive drama queen.
Having had a lot of experience of managing my then un-dx ND, my rational brain would shut down and I'd either be physically sick, pass out, run away or throw the mother of all tantrums. None of these outcomes enhance a dream wedding.
Your DH not attending would be the least bad option.
You are being set up to fail and be the scapegoat when it does.
Reverse it...how about your sister thinks through what would make you being a bridemaid a fabulous experience?
She is being a shit sister.
DH has come up with the only workable compromise.