Your sister is trying to blackmail you with the ‘I’ll never get over it’
she is trying to blackmail you. Remember that.
a small child is neither here nor there in terms of weddings imo. They don’t really understand what it’s about, they can be fun and funny with their shenanigans but mostly they’re just there and can be a pain (truth, not anti kid!)
it’s nice for your sister to say everyone is there for her. To have family pictures, which could happen afterwards if everyone wore wedding clothes for a post wedding shoot. And this is a thing where autistic kids are concerned who just get overwhelmed on the day!
but what if you can’t be there?
you’re post partum. Anything could happen between now and then and you have A SEN child adjusting to a new sibling with its new sounds, smells and division of attention.
It’s going to be hard. Your child may cope for the ceremony then you may have to bail. No pictures for her with you all in.
they may not cope at all
or they might thrive with it all
it’s perfectly reasonable for you set the expectations low in terms of your child for that day. Your husband and sister both need to understand that. Your sister especially.
but remember she is blackmailing you with the ‘I’ll never get over it’