She's an Empress by way of being personally powerful enough to enforce her rules, which are approximately "Don't be evil" and "Don't make me come over there".
Yes, she's trampling all over the sovereignty of the mortal authorities, but the Empress' revised Mandate of Heaven explicitly limits her ability to do so compared to what came before.
Anyone who attempts to object will be explicitly informed of the rules once, and then, if they choose to ignore them, have them enforced.
So far, nobody has decided to test if the Empress has the will and the power to enforce her rules after being informed of them.
Notably, the rules don't require that she does anything if she doesn't feel like it, otherwise, she'd be flitting across the planet, hitting slavers with cease and desist notices.
Arguably, the Empress' return is similar in nature to 1632, or a ship girl being summoned into the less savoury parts of her country's history and enforcing modern rule of law by being more dangerous than anyone else, the difference being that theoretically nobody in modern times disagrees with the "don't be evil" part and her power is such that she's a 300-pound gorilla when compared to an entire nation, not just an army.
The only thing the UN could (publically) claim to find objectional is sovereignty, and who's going to tell the 300-pound gorilla where to sit?
The countries that object in Worm will complain that their sovereign right to be evil is being interfered with, and will be chastised accordingly.
I expect that much of the UN will cheer, because there is a 300-pound gorilla enforcing similar rules that they've lacked the power to do so in the past.