YY, no criticism intended.

Playing music, even if only for a "dress" rehearsal (with an incredibly expensive conductor and orchestra!), takes mental preparation far beyond technical aspects. She probably "panicked" about that more than about her memory of the dots.

The anonymous guest points us to the unfortunate fact that the classical music business concentrates on a very small section of music, the Wild Rovers of Classic, so to speak. The corresponding concerts are a ritual of the bourgeoisie, and good music as a by-product. In most areas of Europe, there are plenty of performances of non-mainstream classical music, with formal and informal dress codes. You just have to look at the smaller posters. Guest seems to live in the USA, where excellent classical musicians abound as well, but there is more desert in between.