"Orpheus was a great musician. Eurydice was his wife."
For the sake of being poetic, but vague. I like this quote. It is very "movie poster"; really telling that this is the story of a relationship. It doesn't sound terribly happy, but gives nothing away. It is also a safe bet for the director. She can go in almost any direction, but this quote will remain relevant.
"One day it would not stop raining."
This quote comes from Eurydice's father when he is describing the day he named Eurydice. He says the letters in her name fell to him like raindrops. I think it excellently foreshadows the whole plot. Rain has a doom and gloom connotation in art, and I feel that it would depict the one on top of the other tragedies that happen throughout the plot. I also like that it was said by her father, bringing in the father/daughter element in the plot aside from the love story. I think it would be really cool if in the poster, the letters of Eurydice's name were raining down onto the three stones.