Remilia knows that Emi is still inside of her, but she is unable of interacting with her, she isn't even sure if Emi is awake like she was while Emi had her body. Using magic, she was able to extend her life and study how to interact with spirits.
Her first test was with the original Star Maiden, she found out from the Spirit Guardians (or something, can't remember how they were called) that the soul of the Star Maiden had been traumatized. Pina suddenly has her body stolen out of nowhere, and then the new owner did horrific things that scarred her for life. Those Spirits that protected her as the Star Maiden tried to protect her soul, eventually separating her completely from Pina's body, now controlled by the reincarnator So the original Pina has no idea about what happened later with the reincarnator, nor the punishment her body went through at the story's ending.
Remilia finds the soul of the original Pina surrounded by her guardian spirits, and makes her an offer: To be reborn has her child. Pina is traumatized, but at the same time she doesn't want to die, and after talking with each other, Pina accepts, and is reborn as Remilia and Angel's first son (we have a gender swap here), but it doesn't seem she holds her former life's memories in this new life, he does come to live a happy life though..
Remilia actually needed someone to test this reborn thing, and Pina was the best candidate, so if something went wrong, she would fix that when it came to Emi. It worked, so later, Remilia finally meets Emi sleeping in this "spirit world" of sorts, happy to meet each other, she did not see anything after she lost her conscience and had her body returned to Remilia.
Emi is then reborn as Remilia's daughter, also seemingly with not much regarding past memories, but she does find her mother beautiful, and Remilia is extremely overprotective and pampering of her, to the point that even Angel feels like an outsider, to which the son (Pina) also agrees with him and finds it a bit overwhelming. In short, Emi is Remilia's favorite child for sure.