The strange poetic nature of this moment is that she carried the fierceness of her uncle but the smiling calmness from her father. Here's the issue: if she's to claim the throne, there'll be ruses that excuse disloyalty towards Yona among Soo-won's subjects; and that is perceiving her as a usurper rather than someone who is able to rule and protect Kouka.
They'd say she'd be taking advantage of his illness to usurp the throne.
But honestly? It's the most logical route to take, especially if Soo-won will die early.
Kudos to the author for making Senju a seemingly 'useless' mcguffin at the Awa arc. Just. Wow. the detailed foreshadowing was brilliant.