Sometimes we make agreements that can be unanimously discontinued. Yeah, it's disappointing and very sad, it will feel terrible and may bring unfortunate consequences, but in this case, for example, if continuing the marriage will bring her to a life of pain until she's old, loyally holding to the agreement regardless of consequences may not be the best choice.
You already suggested the possibility of divorce, but I wanted to reinforce the idea that contracts cannot bind people beyond their ability to follow them without incurring in self-damage, in my opinion, at least.