On p.186, AV says: "Evidently, Elizabeth Shackleton's pride in wearing clothes appropriate to her companions, environment and occasion went beyond a simple desire to impress."
This somehow reminded me of one of Agatha Christie's mysteries, The Body in the Library, where Miss Marple delicately points out that the murder victim can't have been "one of us" (i.e: a member of the gentry in the 1930s), because she was wearing her best party dress even though she had been outside, while a "real lady" would not have dreamed of wearing clothing inappropriate to the occasion, no matter how attractive.
It also reminded me of the book 1939: The Last Season of Peace by Angela Lambert, which Christabel recently recommended at the L&T board, and which is about the last real debutante Season before WWII. Lambert points out that it was very hard for "outsiders" to be truly accepted by this charmed group, because they simply couldn't know all the details of what was considered "appropriate" in clothing, behaviour, etc., while the "real" debutantes would have known these things instinctively, having grown up with them.
So Elizabeth Shackleton's concern with appropriate dress strikes me as not just a matter of what was best for a particular situation, but also as a kind of test of belonging to her particular group, a bit like a secret password!
Just some random thoughts!