Having played that bit just the other day, I get the impression that Nalia isn't offended by Lord Roenall's comment and that her response is joking. I also get the impression that Lord Roenall is more patient and perhaps a little kinder than his son. The Roenall attempt to take over the keep is perfectly legal, at least if Nalia doesn't get the PC to run it. Even then, Lord Roenall thinks that the PC and/or Nalia have cheated him out of something that is rightfully his. Not very nice, but not completely evil either.
I think that the Roenalls offend Nalia by being completely unaware/unsympathetic to the plight of the people below them, rather than by being overtly cruel. Nalia's aunt is like this, not cruel, just unsympathetic. Just after the funeral Nalia thinks that Isaea is cruel, but doesn't think that he's capable of criminal activity.
Remember the trouble she has articulating her dislike of Isaea, so she might also be trapped a bit by the social graces she's learned.