I would have gone with Eliza had she not been Faith..I actually think that Eliza D. would have been perfect as Fray, if it were a few years ago. Maybe she could still work...Eliza's a year older than that Rachel Bilson person...
Summer Glau has the physicality, but...Fray's personality, I dunno...Actually, the character Ana Lucia from Lost reminds me of Fray a little bit. But again, I think Michelle Rodriguez is just too old.
I think it could be done like Sky Captain...everything's green screen but the actors. It would be a challenge to make it seem a lot different than Blade Runner, visually. But, stripped down color like Sky Captain, or even Sin City would be super cool, I think.