Carseain remembered that there was a time during his vacation when he saw Carsina being dragged by the knights in the front door. It was a time when Kina wasn't at the mansion.
He remembered that the reason was she went to the market alone and almost got kidnapped. At that time, Carseain was reminded of his own childhood where he would sneak out and cause trouble, he turned a blind eye to it and dismissed it as something trivial.
Carseain: ' Now that I think about it carefully there were a lot of things that were wrong.
Kina who had never left Carsina's side, especially since the time stepmother entered the mansion, why would she suddenly go somewhere?
Carsina is sickly and I don't think she is actually the type to sneak out as far as I know and concluding what I read in the book, she does not have any acquaintances outside nor has she ever been able to go outside because they always had her locked inside the mansion.