
Nah. I just think they needed a playmate and nurse for their sickly daughter that’s why they took Yiren in. They stopped supporting her once they got Yiren. It’s also possible they simply supported the lady just so they could take in Yiren. With her background she could become a useful card later. In addition to keeping her as a servant basically and locked away they also tried to ensure she didn’t the mentality to ever disobey. Those don’t seem like the actions of someone who cared.

***Spoilers ahead***
She’s basically an imperial heir. Her mother was married to the king. I am iffy about the details but I think it was the previous king. And her mothers family has now taken the throne. So basically she’s the only legitimate heir to the throne now. Her mothers family also took her mother in simply so they could sell her off to the imperial family mince they got close to the throne through marriage they killed off the imperial line and took their place. Killed off the fl’s mother too but she was already dying from childbirth complications I think. She gave her daughter to the counts sister and said the child died during birth.
She could see the fog because 1) there are some powers within the previous royal bloodline that she has inherited. 2) her mother was also contracted to a spirit and it’s implied maybe the contract has passed to her. The spirit is still looking for her mother but she can hear it soo…..also she herself possesses a good amount of magic and has great potential to learn.
Basically the things about regret was all bs because they just want to make her miserable and they do try even after she marries out. Then the fl’s “sister” overhears her parents talking about who Yiren actually is and the idiot has the great idea to go in from the current king (as if that would leave your family unscathed for harbouring a potential heir) but yea that’s how things are so far.
It's kind of surprising that the reason Count Chase kept Yiren was to keep his sister safe. Like, it's pretty out of character from the man we know him to be. I guess he used to love his sister? And he even used to support her too. I wonder what happened? He was a brother who cared about his sister so much that he put is own wife and child at risk. There must be some other reason why he changed.