Here's how the story is gone go in my opinion: She will reject him, then she will get into "I don't like him, then why am I sad about my decision" mood Then Kazuya will start spending more time with Ruka and Chizuru will see them multiple times and feel a "pain in her heart" whenever she sees them, and realizes that she likes kazuya. Of course, that's the case if the author wants to extend the story.
It's dumb, but that's how I genuinely see the story going.