Why Emma Stone?

She's very good and works very hard. Did you know that before La La Land she spent six weeks learning a Mid-Atlantic accent for the film without even being asked? That is hard work. How many other actresses do you know would do that? Then they told her she didn't even need to do it.

She's actually quite good here, and her looks were important for her angel on the outside / cockroach on the inside character.
A bit like an apolitical Milady (the Dumas character).