Roberts is best known for her roles in Valentine's Day, Scream 4 and the Nickelodeon TV series Unfabulous. She most recently starred in the Fox pilot Delirium, based on the Lauren Oliver novels.
Murphy, American Horror Story's co-creator, worked with Roberts' famous aunt, Julia Roberts, on Eat Pray Love. He will also be directing her in his HBO adaptation of The Normal Heart, costarring Matt Bomer and Mark Ruffalo
American Horror Story: Coven premieres this fall on FX.