I think it might be both? A novel and her past life. But if its not a novel then I bet the wish Luca made gave her knowledge of the future in order to prevent it and make him happy (which is my impression of what the wish was, to be happy and have those he loved/died for him be happy)
Oooo. I hope the author makes it more clear
I just read from the raws, and I'll make it short based on my assumptions :
Original Judith following the OG story > Judith got regression and the regression Judith is Korean Judith
.
Meanwhile for Luca..
Luca OG actually reached the mature age but the following story is tragic so he made a wish to regressed > he regressed (so he knows how to read and matured), but kinda shocked with Korean Judith behaviours, because she seems different from the OG story
Here's something that's not clear: since it isn't a novel and, in fact, a life she lived previously, how does she know what happens to Lucas in her absence??