She should be in a Marvel movie...
Who could she play though? Any ideas? Too bad Black Widow's already taken...
Do IMDb a favor and ignore the hypocrite known as MissMisery1313
Sienna will not send you autographed pictures through her twitter. The only way you can obtain autographed pictures of her (other than by somehow seeing her in person) is by contacting her through her talent agencies. She absolutely does have an agent: there is no way around it.
UTA represents hundreds of actors though, from big stars to less famous people, so she probably doesn't have a powerful agent. Maybe that is the issue. Just having an agent is not sufficient: one needs a good agent with the right contacts.
Also, most large roles in studio productions are not open casting calls. A casting director would have contacted Sienna (most likely through her agent) to audition for her roles in Resident Evil or Eragon.