About Irene Adler: I'm sure the real answer was a widespread belief that nobody cares about *opera* so you can say anything. But to fanwank: "prima donna" is used fairly broadly like "diva" today, both in the positive sense ("you are a goddess!") and a negative sense ("you raise hell if there are no hand-painted purple M&Ms in your dressing room").

And Irene Adler could have had a wide-ranging voice, so she could, at a pinch, sing a soprano role but her securest range was as a contralto.