It's not a 100% chance that you will change personas. Most of her moves just have a chance that you will switch from JS to GS(vice versa). I wish we could have a list of which move is more likely to change than others or something like that. For now, just think that 4K is one of the most random...
Guys, i have a silly beginner doubt.
Usually when im in JS i like to combo 3B/66B>4A>4K to switch from JS to GS. The problem is, sometimes the 4K changes the persona and sometimes it does'nt, i dont understand why it is unstable.