I know that the first time I read this one I was so shocked by the Ku Klux Klan concept that it was hard to see the rest of the book. My guess is that EBD got her information from the notorious "South will rise again" romances rather than from Elsie, who made it quite clear that the KKK were beyond the pale.
The other problem I had is with Vera, who must have had all kinds of backstory that told Miss Browne that leniency would have no effect. Unfortunately, we don't see it -- unless she's in some non-CS book? As far as I know, the CS girls never even meet the girl, unless she's one of the unnamed insult flingers; Vera suddenly replaces Doris Potts as Elaine's sidekick on p. 112 with a line on her snobbishness, helps precipitate the "no skating" ban and Maureen's escapade, and then disappears until uncovered as anonymous letter-writer with mind contaminated by impure book. I could understand it if it were Elaine, who'd been piling evil upon evil since first contact, but she meekly reforms after Vera's expulsion. Also I don't think poor Maureen, whom we've come to like via her bonding with Deira and standing up to Elaine, ever recovers, despite her convalescence in the Riviera.
However, I enjoy the way this book builds on prior volumes -- not just larger events like Dick & Mollie's visit, but details such as Frieda's worry over die Grossmutter - and that the quartet begins to gel. Frieda especially gains agency, and who would have thought that Simone would be the one to propose the corn flour incident? The weighing of relative ethics before Joey & Frieda go to the skaters' rescue is classic EBD, and I love Robin's curative powers.
Actually, even in more ordinary illnesses, I'd find singing visitors more healing than those bearing chat or worry.