This wasn't the plan. Jon Green, the general manager of D.J. Stable, and trainer Mark Casse were ready to give 3-year-old filly champion Nitrogen (Medaglia d'Oro) a nice break after her second-place finish in the GI Longines Breeders' Cup Distaff. But just 67 days after her last race, she will go in Saturday's GIII Bayakoa Stakes at Oaklawn, where she is the 4-5 morning-line favorite. Why? Because Nitrogen was telling Casse that she had had enough of taking it easy. "The game plan, initially, was that when she was done...