I wouldn't really expect Mrs. Jennings to give John and Fanny a set-down, per se; it's just that I'm surprised at there not being at least some form of acknowledgment, on her part, of their neglect of the Dashwoods.

I was thinking more along the lines of those half-hearted excuses people sometimes make on behalf of someone who has not acted as h/shee should. No one really believes the excuse; it is merely a form of acknowledging the situation, and conveying regret over the wrong that has been done.

I can imagine her attempting to console Elinor in her usual gossippy way, like so: "Poor Mr. and Mrs. John Dashwood. How difficult their finances must be, what with all the expense of fitting up Norland and making improvements! No wonder Miss Dashwood has not had a letter from her sister." ;o)