Mmm... the only thing that comes to my mind is a lack of "relationship points " , or some kind of missed night scene .
"Relationship glasses" can be viewed in the magazine, and they are depicted in the form of hearts. Also use the "night interactions" on all the girls by choosing those options that you have not previously chosen.
Try to visit your sister in the morning and talk to her . It seems like she should offer to play "bottle".
If that doesn 't help , then ... Has Hanji Zoey left the camp yet ? If not , then go to her classroom in the afternoon , wait for the end of the lesson , and then hug her . She should start talking, and you will choose the option "listen to her" after which Hanji will leave the camp. If you have sufficiently advanced the plot of other characters , then she will return the next day - in this case , you will be informed about it in the diary .