In her first scene, Catherine Vernon is seated at a desk by a window with sunshine pouring in, surrounded by lit candles. Nobody would have lit candles in the daytime - too expensive.
One of the pieces of music - Beethoven's cello sonata 3 in A major was composed in 1808, so a decade after the time the film was set.
Lady Susan Vernon uses the word 'dynamic' to mean 'mode of interaction,' or 'quality of relationship between persons,' a usage that was not present in the English language until 1978, two centuries after the time of the story.
Lady Susan puts perfume in one hand, but smells the other.