I would argue that the biggest example of naturalism in this impressive novel is the way in which Edna as a character seems so moved and influenced by the various whims that she experiences, especially when she hears music. Consider the impact that listening to Chopin has on Edna:
...the very passions themselves were aroused within her soul, swaying it, lashing it, as the waves daily beat upon her splendid body. She trembled, she was choking, and the tears blinded her.
Simply being able to feel the music at a subconscious level, we can see the way in which the music creates whims in Edna's character. It is these whims of course that she acts upon as she struggles to express what she is feeling inside of her and how that can be translated into the exterior society of which she is a part. The above quote, for example, is from Chapter 9, and comes after Madame Reisz plays for the company. In Chapter 10, as a result of listening to this music, Edna finally learns how to swim. The music that stirs Edna so corresponds to a change or development in her character that sets Edna against the laws of the universe that are embodied in naturalism, placing her on the road to disaster.