This is absolutely awful, especially since the reason your DC won’t have their dad there is because he’s passed.
So you’re good enough to pick up the cake, but not good enough to be there for the whole weekend?
Being the only one of the six excluded is absolutely awful. And by the way, I’m AuDHD so she can fuck off with her “little bit autistic” excuses.
I really don’t think you should go. It’s humiliating to be thrown a few breadcrumbs. You deserve so much more than being treated like second best.
Have you replied to her yet?
Do you have other friends - is this your main friendship group?
Will refusing this event blow up the friendship group for the future - and if so, do you care? As it’s one of the rest of the group that’s asked you to pick up the cake they clearly all know you’ve been left out. I don’t think these are your friends - they’re treating you like a hanger-on.
I wouldn’t go OP - I think I’d say something like “Being the only one out of our group not invited for the Friday is a bit humiliating, tbh. To avoid any awkwardness on your weekend I think it’s probably best that me and the DC bow out completely. I hope it goes well.”
I wouldn’t demean yourself by going OP. I’m so sorry this has happened 💐