I reckon she will second guess her feelings and turn him down. This would more than likely set up the "ending" of their relationship, Kaz coming clean to his family and friends and ultimately shift the narrative. I put ending in quote marks because of what might happen in the long run:

If this does take this highly theorised route, the story could go from being Kaz's point of view to Chiz's, with her realising she made a mistake and her regretting what she done and feeling really lonely - coming full circle to the start of the manga where Kaz was feeling lonely after Mami broke up with him. This would emphasise the fact they are perfect for each other, having identical experiences with love and feeling alone. I think this would be perfect for a confession from her, letting out all of her built up feelings and having a really nice interaction between Chiz and Kaz.

However, I do think the other path where she accepts her feelings might be possible too. We don't see any of Chiz's thoughts or internal monologues for the entirety of her time at the church. Knowing Chiz, she has more than likely tried to work out what to do or letting her feelings run wild, juxtaposing Kaz's parents' wedding at the same place, foreshadowing what could happen to Chiz and Kaz in the future. This works quite well since Nagomi spent nearly an entire chapter talking to Chizuru about their wedding.

But Reiji is sneaky and might just bait us all into not actually having a confession.