Lissa would def hop aboard this argument, if you need more people! She'd add an anecdote of her own, in that her father continued war and it absolutely destroyed their people's happiness and trust, to the point that their people didn't trust the ruling family for years....all for the made up faraway nations that they're supposed to be representing, of course, and not these real countries from distant worlds.

If this doesn't actually go with the angle you're going for that's cool too, she'll just +1 everything said and lend her nonexistent weight as a princess.