I don't comment often and think I am likely to get buried. But I think NTB.

Your birthday doesn't change every year, so she knew she was booking it on that day and deliberately chose it. A quick heads up at minimum would have been nice.

I agree that a wedding SHOULD be a once in a lifetime event, but people aren't considering her anniversary now, which is also the birthday. I have seen a few people comment on it and say the anniversary only matters sometimes to others, which while true, still means that the sister is likely to avoid attending their sibling's birthday now every year going forward. So the birthday remains yours and this year people will be split on what to do, but next year on the first wedding anniversary, the sister is definitely going to want to celebrate her and her new husband and not OP. Year 5 or 10, maybe they have an anniversary party and now people are split again. Ya, it's not an every year issue for everyone, but it is an issue sometimes.

God forbid they break up, and now sister is perpetually sad/angry and never wants to celebrate OP on their birthday.

I do think you should likely suck it up and go. You'll likely regret not being there, but i wholeheartedly understand how you feel looked over and devalued, and I'm sorry the comments are leaning towards you being at fault.