Hi, thanks for reporting this bug. Unfortunately I was not able to reproduce this issue (see screenshot).
It's possible that this is an inconsistent issue. Please go to B4 with Paila again and let me know if the moon herb appears. (If you exit/you die/she dies, Paila will reappear on B2 the next day and you can try again.) Also, please check that the game prints "Apparently the moon herb is on the middle floors" when entering B4.
