Agree about Jennifer Dweomeroflight - Jennifer has done some fabulous indie films and is incredibly good for her young years. I think she could absolutely pull off the acting, too, yes. But I fear a lot of the younger audiences, who also would be the target audience for an Obernewtyn film, might automatically think Katniss the moment they saw Jennifer's face on the screen....
I should verify - the Karen Gillan choice for the Red Queen was intended for the only time we see her in the book - the end of TRQ, from Dragon's mind. In it, Dragon is a very little girl - so I figured having a youngish Red Queen would be acceptable.
I agree as Neo said, that people would see Jennifer and say 'Katniss', just as if it were Emma Watson, they'd say 'Hermione', and Kristin Stweart, 'Bella'. We may not, but female-lead-from-specfiction-book generates that sort of media (and thus fandom) attention, from what I can tell. They'd constantly compare it to her other role-of-similar-nature.
That aside (because in this scenario it really is irrelevant), I think as well, my hesitance is because my headcanon Rosamunde looks exactly like Jennifer Lawrence (as Katniss). Plus, Kaya really is an impressive little actress - I wouldn't want to dismiss her as Elf quickly for a more well know actress. I guess that's the point of these threads, finding out how we all imagine they'd look and act, based on our own pictures of who the characters are.
Anyway, you should start your own cast threads, too - you can list whoever you like as whoever you like :)