Take a look at the various clips at the Dreamworks site - behind the scenes and making of stuff. Jennifer Hudson gets plenty of respect. It's her first movie - her billing is appropriate.
If Tatum O'Neill can win a supporting Oscar for Paper Moon, or George Clooney in Syriana, or Geena Davis in The Accidental Tourist, the logic follows for Effie White to be a supporting character. If Nicole Kidman can win a lead Oscar for The Hours, the actual size of the role has less to do with categorizing performances than the name attached.
This looks spectacular.
"Love Life. Live." Michael Bennett