I must agree with the previous post talking about The Walking Dead. She would make a great character and important characters are coming in season 5, she have the acting skills, the shape and of course the fight ability to play a character in this show. This is pretty rare that they choose actor/actress that had big role before, but still, it would be possible. Darryl, Michonne and Summer, they would have a pretty badass team
I think my choices would be Defiance, as one of the scaly votan which I feel guilty for not remembering the name of their species (as much as I want to see her in non scifi roles I do still want to see her in scifi every now and then)
Supernatural, as a hunter (I can just imagine it, summer running in the middle of the night, struggles to try to open the front door only to get grabbed and thrown through it into the house, three demons walk in looking tough, then she pulls out a mini torch and aims it at the roof, the demons look up to see that the torch is projecting a devils trap, she starts reciting an exorcism and the demons start to smoke out, role the opening)
and Shield as an obstacle in the fits/Simmons relationship. (I've always shipped theose two, I just hope Joss doesn't kill one of them right after they get together) she would be gunning for Fits of coarse.
I agree, the Castithian are very looking like the ''bad guys'' in the show, but the whole species isn't like that. She would be great in this universe, plus she would look beautiful in those colors :P