As soon as Serena f-d the official she was guilty of a code violation. It being her second, she forfeited a point and therefore the game.
In an earlier match this US Open, she repeatedly eyed down a linesperson who called a foot fault in an effort to intimidate them. No one said anything and the announcers laughed it off. Well look who's laughing now. Anyone who dislikes Serena has plenty of ammo.