in secret zaofu is referred to as not part of the earth kingdom but isnt it? like yeah it's isolated from the rest of the mess but It's still part of it.

Interesting question! As I've always understood it, Zaofu is autonomous in its governing. Su runs the city herself as the 'Matriarch', refers to herself as it's leader, calls it her city, openly trash talks the queen, and the wiki refers to Zaofu as an "Autonomous City State". So geographically it's within the Earth Kingdom, and I'm sure before Su bought that plot of land, the empty land itself may have been technically under the sovereignty of the Earth Queen, but apart from when Kuvira invaded, its government has always been separate from the Earth Kingdom. And I think once Kuvira was defeated and Wu took over, he would have just handed Zaofu back over to Su. But, it's not a democratic city, Su is in charge.

So what I was mentioning in Secret, is that Su would be very intrigued by the fact that Wu is doing exactly what she was trash-talking Hou-Ting for not doing: Abdicating and reforming the Earth Kingdom to help it evolve with the times. And with that in mind I think Su would be curious about the progress of the democratization and consider reforming Zaofu in a similar way, and then joining under the umbrella government for the Earth Republic or Democractic States or whatever they're going to end up calling it.