Saw a mdzs fandom post suggesting that chengxian be tagged as incest. And now I'm imagining that Madame Yu would be so against the idea of people believing that Wei Wuxian was part of her blood family that she would actually set up a betrothal between him and Jiang Cheng just to prove it. Not with Jiang Yanli, though; her girl deserves better.
she may hate wwx's guts but even yzy will admit that wwx is skilled and devoted to jc and would die for him, and thats really her most important requirements for jc's spouse