Somehow, I didn't understand on my first read-through of this chapter, but having read it again, I see, now.
So the duke actually wanted to keep the family in a neutral position in the succession war between the two princes (as his wife mentioned on the
seventh page & which I somehow missed the first time reading) and his original "punishment" plan of sending his daughter to a nunnery was actually done to both keep her safe from harm as well as prevent her from being used by either side in the succession war. "I thought that if she has to be dragged into that mess of a succession war, then it would be better to just..." It would be better to just send her away to be a nun.
He changed the "punishment" to leading the fiefdom when his daughter proved that she might have enough intelligence to hold her own and, therefore, he might not need to protect her as much as he first thought. It gives her a chance to prove her abilities and show that maybe she won't be as easily used and influenced by other nobles for their own ends in the future, which is what had helped contribute to the cancellation of her engagement.
@ the Sebas comments: Many Japanese authors (in particular, isekai authors) are guilty of two writing crimes: First, they are unoriginal at naming their characters. Second, they often shorten the names, even if it looks weird.
This explains why there are so many butlers named Sebastian, and why the name is often shortened to Sebas. Isekai authors are lazy fucks. (lol)