At one moment the tune "Du und Du, op. 367" is played, which at that time was considered as written by Johann Strauss Jr. but based on current investigations was actually written by Eduard Strauß. The tune was written in 1874 but the movie is set in 1815. The tune was also not a part of the operetta which the movie is based on.
When Melanie is walking through Vienna she hears a waltz and is asking what kind of new music this is. The movie is set in 1815 during the Vienna Congress and Melanie said that she hasn't been in Vienna since 5,5 years. The Vienna waltz however is considered to be introduced in around 1800 and the term "Vienna waltz" was first used in 1807. So it shouldn't have been anything new for her.