never satisfied with the day unless she spent the chief of it by the side of Mrs. Thorpe, in what they called conversation, but in which there was scarcely ever any exchange of opinion, and not often any resemblance of subject, for Mrs. Thorpe talked chiefly of her children, and Mrs. Allen of her gowns. (Ch. 5)

I have never seen Henry’s reply as rude before but I see your point that it could be interpreted that way. I don’t think his intent was to say it looks like cheap muslin but that he can recognize different qualities of muslin. I think three things come into play about Mrs. Allen—her general silliness, her self-absorbed, inattentive and single-minded nature and she does have an eye for dress and accessories that is unmolested by the narrator. In Ch. 4 Mrs. Allen only appears to listen to Mrs. Thorpe’s maternal effusions while she is actually ruminating on her favorite subject which eventually gratifies “with the discovery, which her keen eye soon made, that the lace on Mrs. Thorpe’s pelisse was not half so handsome as that on her own.” and in Ch. 5 she feels about the Thorps “as the completion of good fortune, had found these friends by no means so expensively dressed as herself.” Perhaps Mrs. Allen is not offended by Henry’s remark because she is confident that her muslin is nice and she is unable to conceive his meaning being anything but exactly what agrees with her own thoughts on the subject. She takes Henry’s remark to be a compliment on her genius in obtaining such amiable muslin at a good price because she is enjoying a great deal of self-congratulation on the purchase. I think Patty Patricia is correct in labeling Mrs. Allen obtuse.