Kurumi's Star Festival did kinda imply that clone would come back eventually, she might use the little time she has to get some information to Shido, information that will help Shido finally get through to her.
Or maybe the Refrain doesn't apply to Kurumi herself, but the DEM. They could get in the way and put a stop to both Shido and Kurumi's goals.
Summary looks to be out from amazon and placed on the summary of Vol 16.
Make the Spirit that he was unable to win over in the past, fall in love!?
The Spirit who returned to Raizen Highschool----Tokisaki Kurumi. “----Between me and Shido-san, whoever falls in love loses……so how about that?” Kurumi who desires Shido’s power and Shido who wants to seal Kurumi’s power. The second battle (date) betwen the two of them begins----