Xiao'er knew that Shangguan Xuanyi was under great pressure. In reality, it wasn't quite the right time to attack Nangong Country, as Minze Country had only just begun to develop. If they failed, returning to their original state would be the best outcome, the worst-case scenario being the extinction of their country due to a careless mistake.
For them to conquer the entirety of Nangong Country, they would have to rally the entire strength of their nation, an endeavor that posed quite the challenge. The reason Shangguan Xuanyi suggested attacking Nangong Country was merely for his own protection. Had it not been for the relentless attempts to harm him and take his space, Shangguan Xuanyi wouldn't have been in such a rush to act.
While Nangong Country was preparing for war, they too were making preparations. If they could have another year or two to get ready, things would be much easier.