Paul goes to a drugstore to buy it for Penny. Thanks to the screencap above we can see its bottle is actually the one of a historical and extremely popular perfume, Evening in Paris by Bourjois. The cobalt blue bottle with the curved label began appearing in the late 1940s/early 1950s, so the choice to use it is historically accurate. A cobalt blue talcum powder bottle of the same scent can be seen on the drugstore shelf, too.
As a revenge, she badly wounds Paul: she straps him to a bullseye wheel and stabs him on purpose. Penny arrives to the circus and finds Paul fighting for his life. Elsa immediately realizes she’s the one Paul is having an affair with. “Speaking of cheap perfume” conveys her contempt for the perfume and for its wearer (let’s not forget she wears Caron Nuit de Noël), but also her envy for the two star-crossed lovers.