I knew she's going to have feelings for the MC, but it's still a little jarring to see how out of nowhere she goes yandere mode with him without any real indication that she's ever had feelings for him. We only knew beforehand she'd have feelings for the MC because every hot, important female characters always have feelings for the MC in these types of manga.
Also, the audacity of her to try to make the MC hers when she's in danger of becoming a sex slave of the royalty at any moment. Not like she can refuse because her entire nation's people are being held hostage.