The thing with movies is that they never get it right...I don't think they can capture this woman's essence, who can really? and maybe that's alright. although it is a sad thing that people might get the wrong idea of who she is.
Jaquetta has the credibility for sure, but the sad thing is she's not an actress.
A really good actress should be able to chameleon switch it, so their is no sense of themselves in the role, but all character...your not paying attention to the celebrity of the actress but to the words and feelings she's communicating like Tilda Swinton, Cate Blanchette or Parker Posey. I don't think Sienna is there yet. The only parallels i see is the 'It Girl' factor that both of them have. and that shouldnt be the basis for this character choice.