After Shelby bludgeons Matt in the basement and is dragged off of him by Dominic, you can tell Matt's legs are not that of a real body, as they react to Shelby's weight much like a rubber version of a body might.
Shelby's uses both arms equally strongly just hours after being severely wounded. Likewise, the wound does not open and bleed even after extremely vigorous use of her left arm.
Sarah Paulson addressees Lily Rabe as Lily whilst dressing her arm, instead of Shelby, her character's name.