Sorry, but you both need to start the quest at the same level, otherwise it's automatically downgraded as you've found out and by then it is too late to do anything other than start over.

I appreciate that it's not much help to you now, but they do actually warn this on the Eternal Bonding pricing page: http://www.finalfantasyxiv.com/etern...?lng=en&rgn=na

So yes, you basically need to completely start over (abandon quests, throw away the wristlets and buy new ones).

Sorry I don't have better news