This is what they call a fait accompli. By announcing the whole truth in front of the entire congregation, not only will there be no wedding, everyone will know why, and no one will consider her fit for marriage ever again. There are many ways Edward or her parents could have tried to prevent this from happening - but now that it's done, the repercussions are irrevocable. She is finished in high society. The worst case scenario she was trying so desperately to avoid has come to pass. And the world keeps spinning. Multiply that by a thousand and that's how a society changes. Many, many people doing the previously unthinkable until it becomes thinkable.
But really, couldn't it all have been solved so much sooner if Alice had confided in Jean from the start? In the end it seemed it wasn't Alice realizing that being true to herself and her love for Hanako was more important than anything in the world that tipped the scales. It was her realizing that the only people she would truly hurt by blowing the whole thing up in a spectacular fashion were Edward, who was a dick anyway, and her parents, who had it coming. Maybe it was sisterly envy all along?
"What do you mean, you're a suffragette now? You're trying to out-feminist your big sister?! Anything you can do I can do better! Hold my bouquet, I'm going in!"