She's serviceable. Because of her, we got to see how far Orochi's treachery encroached and corrupted the country, and how she and Denjiro needed to fight that corruption by dirtying some of their own hands. It sold the desperation the Kozuki family was facing in the midst of the power struggle until now.
She herself is fine, but her lack of a role in the arc kind of guts her considering her status as a Kozuki. She only exists to move the stories of other characters, like Denjiro, Zoro, Momo, etc.
There's nothing really between her and Zoro, imo. Like Toko, Tama, the people of Ebisu, and even Tsuru, Hiyori is just another citizen of Wano Zoro is fighting on behalf of on Onigashima. And among all of them, Yasu left the biggest impression on him.