First of all, the reason why FL acts like Luca's mother is to protect him while she is with him. Because she comes from a low-born family. She thinks that if she tells the duke's family that she is his aunt, she will be sent away and the high society will not be able to protect luca.
She thinks about Luca going back in time in episode 90 or so. She doesn't think about it beforehand, she's trying to get used to her own life and I think it's because she thinks luca's character written in the book doesn't match up with reality or he's trying to act more like an adult around her aunt when her uncle is also there.
And in the beginning, her aim is not to die. (according to the book he read, he was deceived for money by relatives who wanted to take over the duke's seat and were eventually killed.)
Who wouldn't want a ml like this? He loves fl. He takes whatever she wants or doesn't want. He protects her. He's handsome, rich, has a good family and he loves Luca enough to die for him. (According to the book FL read before she was reincarnated, ml was dead)
Also, if I remember correctly, in the 100-110th episodes, she tells the full reincarnation events etc. Sorry for my English, I used trans.
P.s. She thought that Luca was reincarnated in the 19th episode, but the personalities of ML and his mother are different in the novel, so he thought that Luca might be different too. She also thought that she could not ask questions such as "I have reincarnated. Have you also reincarnated?"
First of all, Luca with his “I’m not a child” attitude he definitely went back in time or something his character is too different from the original.
It was even hinted but for whatever reason Judith doesn’t think it’s possible??
Then we have Judith who not only lied about being Luca’s mom (someone please remind me why she did this) but she decided to stay with him even after seeing he’s not the original cute kid and can look after himself… like gurl what is your purpose??? Also would have liked no romance. At this point she’s just there for the man… who wouldn’t be.
Thank you for hearing my Ted-talk (●'◡'●)ﾉ