@Purplelibraryguy I do agree with the fact that calling her a bitch kind of dismisses the actual danger of her personality. However, I still think knocking her out and putting her in jail was the correct choice. They could have had someone slightly more important/qualified guarding her, but she has too much info to just kill like that. She's not actively bloodthirsty, she was trying to negotiate and then escape when that failed. As a reader, I'm more biased by the fact that she has a squirrel, not the fact that she's a pretty girl.
Also, ethics are important in the first few big decisions of a new ruler. Contrast the style of leadership of the two - killing Nyan-nyan would cement the policy position of the current government in the Soo-won direction, while keeping her alive would push it to the Yona side. I could describe the contrast in plenty of different ways - logic vs emotions, structure vs flexibility, science vs faith, conservative vs progressive, bureaucracy vs democracy, birth vs merit, growth vs stability, war vs peace - but if I picked one I feel that would be imposing a judgement in and of itself given how much connotation most of the terms carry. Anyway, the point is that it's not about is the girl good or bad, it's about what direction this story as a whole wants to go in.