Just a random casting, which is original!
I chose the new actress, Nicole Fox.
She was REALLY great in the short films I have seen her in, and is starring as a self-mutilating teen in the film, Sprawl. I think she will do GREAT things!
She is also a martial artist, and has done gymnastics, which would help due to Mercury's....Lithe body.
Mercury is also an AWESOME character, who is completely underrated!