So as I said in earlier chapter
Spoiler!
So this girl is Rania.
The previous Duchess was a commoner. They said that she passed away but she actually ran away. Rania is a child she was supposedly carrying that time. Camilla meets Rania when she doing her "Volunteering Club".
Fastforward, Rania invited herself to the Duke's manor and introduced herself to the Duke as his daughter and she called him "Father", but the Duke feels a little uncomfortable with it because they literally just met and she's already calling him dad.
Rania kept trying to sabotage Camilla. She would intentionally steal her seat at the table, she take Camilla's tea time with the Duke and she basically tried to win over everyone on Camilla's side (and failed). However, she is actually a fake Rania.
She's someone who possessed Rania's body (real Rania is dead). Anyway, fake Rania's ploy didn't work so she first tried to poison the Duke, but he recovered because Camilla gave him the antidote which she got as a gift from former patriarch in exchange for finding the divine beast. Next, she kidnapped Camilla and assumed her face, but real Camilla showed up and basically Fake Rania was exposed.
The previous Duchess was a commoner. They said that she passed away but she actually ran away. Rania is a child she was supposedly carrying that time. Camilla meets Rania when she doing her "Volunteering Club".
Fastforward, Rania invited herself to the Duke's manor and introduced herself to the Duke as his daughter and she called him "Father", but the Duke feels a little uncomfortable with it because they literally just met and she's already calling him dad.
Rania kept trying to sabotage Camilla. She would intentionally steal her seat at the table, she take Camilla's tea time with the Duke and she basically tried to win over everyone on Camilla's side (and failed). However, she is actually a fake Rania.
She's someone who possessed Rania's body (real Rania is dead). Anyway, fake Rania's ploy didn't work so she first tried to poison the Duke, but he recovered because Camilla gave him the antidote which she got as a gift from former patriarch in exchange for finding the divine beast. Next, she kidnapped Camilla and assumed her face, but real Camilla showed up and basically Fake Rania was exposed.
So in short she a bi*** 
I like to post spoilers for the stories I find interesting because I don't have much time to read novel due to busy schedule you will find me in most romantic historical manhwa comment sections
