I don't get what's that unusual about what Yona did... She did what she always does, she puts herself on the line for protecting those she loves and cares for. She admitted in this chapter, that none of it is for su-won, she doesn't feel bad at all for his sickness.
She's not letting go of any development or anything, she's found a way to expand her boundaries, in a way that would be agreed to. Avoiding all the problems....
She did say in the last chapter, she feels as if her legs have been cut, I know it's because of the restrictions, but she's working herself out of it, without any help from anyone (she even went to see su-won incognito, can't say she didn't learn anything now, can we?).
She's the kind of princesses who would want to rescue herself, rather than put someone else at risk (much less if it's someone important to her)
Logically speaking, the story is headed in the right direction, I expected something like this to happen sooner or later, and things might look bleak for a while, or longer, but that'd just make the happy ending even better, trust me.
And lastly, we finally see Yona's first enemy(as per the manga) , #1 villian from chapter 1(the only villian except su-won, which pretty much made us forget him) , who scared Yona before her birthday 😤
Su-won should at least punish him for leaving those nasty bruises on Yona's neck 😡 though I know he won't, but if Hak or anyone from her group saw, they'd definitely be super mad, just like I am.