] However, I was alarmed when "she judged it right that they should sometimes see their brother" when he arrived in town. Does she really believe that her distraught daughter would feel any relief in the company of John and Fanny, for whom Mrs. Dashwood has such contempt? This question has me doubting the extent of Mrs. Dashwood's wisdom. Have I misread something here?

In this case, I think Mrs. Dashwood is showing higher principles and greater generosity than her step-son. In spite of his treatment of them all, Mrs. Dashwood (and I'm sure, JA herself) would feel that a complete breach with a member of the immediate family would be a (morally) bad thing. She knows that her daughters like him no better than she does, but he's still their brother, and she is advising them to see him the minimum number of times necessary to keep the connection going. (Of course, there was also the matter of "not washing the family's dirty linen in public" - a bigger consideration then than now - it would have been considered vulgar to make a family quarrel public knowledge).