She's not your girl next door...
" Any woman asked to wear head-to-toe latex is going to experience a little gasp of panic, but it’s fun. You actually forget you’re wearing it after a while, but other people sure don’t. I’d bend over to tie my shoes and four grips behind me would be making groaning noises and suddenly I’d be quite aware again."
Kate Beckinsale

She can do glamour

After seeing these pictures of her from Halloween '04, how can you even imagine anyone else? She is even quoted as saying she would like to do the part:
"I dressed up as her last Hallowe'en so it would be good to do it again."
Hey, Joss Whedon, if your reading this (and we all know you are), I think it's obvious who we need to play this part.
+ Her accent helps!