It happens the first time you go to Kitty's room after Laura is back. It doesn't happen if you are invited to the room. You won't be able to get in the room unless Kitty likes you enough, though it doesn't take much, it seems. It makes the most sense story-wise to do a few days after Laura is back, but if you have a high-enough rapport with Laura she will also change in front of you.How do you unlock that scripted event where Kitty is putting Laura in new clothes? I feel like I "missed" the event. It has only worked once for me. This playthrough it just resulted in Kitty saying, "Come back later," but then just collapsing after that.