Yara MADE this film!
She was the best part of it.
The (white) people quipping that she was too angelic and sweet to be believable just have race problems. Can't stand to see a beautiful, talented, and mannered black child. And white Hollywood agrees with you--which is why Yara ain't on the cover.
She made this film was it was and was a great FOIL to Jen Garner's (also pretty unbelievable--but it's okay because she's white, right?) character, which was the point.
Also--why wouldn't an abandoned and tossed around foster child NOT be quiet and kind? She's essentially trying to get these foster parents to love her and not want to throw her back into the system. Her disposition made sense, and that added with the normal Midwestern, easy going, all-American personality, it made a lot of sense.
Consider all the haters racist. Without her this movie would have been crap.