Hi there! Once you've done the buffet event with Zoe, after you visit her in her room and see her at stage 1, Gwen's shop now sells a weaker version of the restraint brew! Buy some, and put it in Zoe's room. Zoe will then be able to be called over to the Buffet, as long as she has restraint brew in her room! (She consumes 1 per day)