Well, for starters... *modifies post attempting to kick off fight because he didn't think it could be resolved peacefully*
We could see if there's a way to convince her not to touch the portal. Tough, but might be possible.
We could also call Yuuka's cutting over here... Unless she can't come for some reason.
We could try selling her on the natural order of things <---- Not even if Higan froze over would this one work.
Try dragging along Cirno and letting Gengetsu use her as a punching bag <------I get the feeling attempting to leave would spark off the battle.
Try seeing if Malus can somehow get the point across <------ Not likely, but worth a try
>"If you really don't want there to be a portal to your world, you could always simply just isolate the portal area, cut it off from the rest of your world. That would prevent damage to the portal and other worlds, while at the same time preventing others from truly entering your world."
I don't think this will work. She's already made it clear she hates the very thought of it being there. We'll need to find a way to completely isolate her world from the portal. Otherwise, we're gonna have to fight it out.