I never expected this kind of a question in here! :D
But let's see if we can help out a bit.
The peace you lack is because you can't accept that she disagrees. You are struggling to be right, and so is she. Perhaps some clarity would help: she's the only one who can clearly tell you her feelings on this, so she's the one you have to talk to in order to resolve this.
The pain is because you are trying to have control over the situation (based on your explanation of things). And so I would recommend meditation on why you feel the need to control and dominate this decision. It's not hers; it's yours. You are the one who has to live with the consequences of making it in either case. Except that she believes it also impacts her (and she wouldn't oppose it if she thought it would turn out well).
Consider her input, find out if she's willing to help you understand, and by all means listen! But if she isn't convincing to you, consider what it is that she's seeing, and try to come up with a way that it won't be an issue for her.
Generally, there is no way to avoid conflict, but if you take it from a position of having her explain her reasons to you so that you can understand why she's so opposed to it, you may find a solution you're looking for and avoid further issue.