YTA, you suck for going back on your word. Of course she needs to know how much you will contribute. Budgets are crucial in weddings. Also, you should not tell your daughter who she should/shouldn't marry, especially since she's such a "bright, smart, headstrong young woman."

And what do you mean they didn't tell you? How was she supposed to know she was about to be proposed to? Also, the old tradition for asking parents for their daughter's hand in marriage is antiquated and no one does it anymore.

There's no info on how involved you are in her life and how you voiced opinions about her Fiance in the past. Feel free to back out from the wedding, but be prepared to face the consequence of losing a daughter while you're at it over your little fit.