Not what I expected, but so very intriguing . . .
A regression? This is clearly not the Judith Maibaum from the original novel, she gets on far too well with her sister and isn't jealous. But at the same time, it's not clear whether this is recovered memories of our Judith's first time around the reincarnation wheel, or if it's something else. Presumably we'll find out once things progress to the point where Reudiger comes to find Luca . . .
But given Luca regressed, where does he fit in this? If the Judith in his original timeline was this reincarnated Judith then surely his timeline would have been very different - even if she doesn't end up meeting Reudiger she's still not going to be the abusive aunt that she was in the novel . . . But even if she wasn't abusive, in this scenario she might not have enough recollection of the details of the novel to be able to change things meaningfully . . .
So . . . . . maybe this is the Judith of Luca's original timeline? Maybe that's why he was so willing to glom onto her when Reudiger showed up - this is the Judith that he knew first, and our Judith, the one who was isekaied and recalls all the details of the novel, is the Judith of his regressed life . . .
That would mean the original novel was being changed from long before we started seeing anything - Judith's reincarnation would be the starting point, a whole lifetime before we saw her supposed car accident and death.
. . . oh, hey, quickly checking the first chapter to review a few things I noticed that even back then she didn't have a proper memory of her death - neat, always nice to know they plotted everything out well in advance.
Anyway, it all starts waaaay back when our Judith was young, and had questionable taste in literature. She read the orignal novel, loved it, and almost died . . . but then lived a full life afterwards and died peacefully . . . only to be reincarnated into the novel she loved so much back when she was a silly college studente. As happens with these things, the novel world started changing once she was reincarnated into it - she was a loving sister to Lalisa and a caring and loving aunt to Luca, and although her second life wasn't great it was at least pretty decent.
Maybe she remembered a bit about the novel when she saw Reudiger coming to collect Luca or maybe not, but she read it a lifetime and a half ago, and only had vague memories of the plot - she wasn't able to change things much, being less greedy but more naive, and far more easily manipulated. So she dies roughly the way the original novel went, and so does Reudiger, and eventually it all ends with Luca surviving at great cost . . . and then he regresses. Maybe he regresses to the point where his mother died or something like that, it probably doesn't make much difference, but he finds his beloved aunt is . . . different.
Time passes, and he's both confused and angry, but then suddenly she changes, and while she's not quite the same person he remembers, she's clearly not the person he's been living with for years. Maybe he suspect she, too, regressed - after all, he wouldn't have seen her in decades by the time he finally regressed, maybe he wasn't quite sure if she was different from his memories or if his memories were just too vague. But she's not the selfish abusive woman he was living with before, and she clearly cares for him, even if it's initially just a decent person caring about a child in their care. Regardless, that's where our story picks up.
What that means about the point our story starts I'm not sure - possibly they both regressed back into the world of the original novel, just waking up at different times. Or maybe it was all reset right from the beginning, and Luca was reincarnated at the end of his life (possibly not long after the novel ended, given the type of novel it was), with Judith being regressed back to some random point during Luca's early life. Or maybe there's another intriguing twist in store for us along the line . . .
. . . of course, that's all speculation . . . but it's such fun to speculate about a well plotted story like this . . .