Firstly, a bit of absinthe appreciation wouldn't go amiss. As the illustration above shows, absinthe was huge in the artistic circles of Europe at the time, and it made it's way into their illustrations. In your look you can do this by featuring the green fairy herself, or by adopting shades of emerald and peridot. Still more interestingly, you could add absinthe motifs, like the below Alchemy Gothic slotted spoon necklace.
When one thinks of the Goth look, one (probably) doesn't think of a neutral look. However, Art Nouveau ladies are rarely spotted sporting heavy winged eyeliner, so to mimic their naturalistic grace use lighter eyeliner, maybe a bit of blush, and a pale lipstick. Keeping your hair in either a messy bun or long and slightly curled will complete the look.