So I'm assuming the "Heroine" had another soul forcibly put in her body, leading to there being something akin to split personalities. One being the original Heroine and the other one. While our MC was natuarally born into this world. Memoies were put on hold till the finale moment, leading to a situation where there isn't any forced soul in the body. One of the is a body with two souls and the other is a body with two entire life's behind it.
Honestly, that could be an interesting idea for a manga to do. Dedicated to the difference in being sent to different words under different methods. How it affects the person(s)
I like to imagine that the Lucian goes and leaves the Monastery. Maybe she finds some magic or something. She has a kid, maybe with a random nobody, but just to have a kid. Then puts the other ones soul in the baby. I love the idea of them living in the middle of nowhere on a small farm. The original heroine enjoys her life. While the other one is in some type of hell. Imagine it. Having to go through childhood for pretty much a third time. But this time from a baby. Someone like a stalker pretty much forcing you to breastfeed and grow up with. This could be such an amazing body horror type of story. As you get older the stalker gets more and more intimate with you, despite technically being the child of the stalker. In the end, she's still the heroine, and has a bunch of cheats unlike others, which she uses to spend her time with the other one. Such as always hunting her down whenever she escapes, and immediately being reborn. Maybe some weirder scenario. Where the heroine takes over the daughters body once it reaches adulthood, and sends the other one back to being a baby.
Fyi, I'm tired, you can ignore most of this. I'll probably wake up and wonder what tf I wrote.