They can have a firm and unified front without getting hitched. As it stands now, their fates are tied together already. Nama is the Empress, it's her call, and if she decides to sign a treaty and stand with Youmi, I don't understand why there needs to be a wedding attached.

[She tips her head to the side for a moment because this whole idea makes her skin crawl for a lot of reasons.]

Signing the peace treaty will make the rebels angry. Marrying Youmi will make the rebels angry. Either way, the rebels are angry, so why are you so intent in pushing the idea that makes it seem like the only value these women have for diplomacy is if they're married - it doesn't matter that it's to each other.