Obtaining a persona/having a shadow is honestly different for every game so Kotori having her own play out different in her dreamscape is fine! P3 had them simply accepting death and shooting themselves in the head with their Evokers (a fake gun), P4 accepting their Shadows, and P5 had them "breaking the chains of rebellion" and their Shadow sort comes out from that, creating a mask and once its ripped off their faces (just as gross as it sounds) they get their Phantom Thief outfit and Persona.

So how will Kotori's play out?