I think it's interesting that Carol is giving Corina false information since at the beginning of this chapter, Corina reads that "Avril is living in an annex away from the main house (sorta true), is ignored by the servants (false), and has never met the Duke (hilariously false)"
So it seems like a sign that Carol is fairly moral if her family wasn't held hostage in some way, or extremely dense to not notice how well Avril's been treated.