Padua Stable's Freedom's Daughter, winner of the Schuylerville Stakes (gr. II) in her second career start, died Monday after suddenly becoming ill over the weekend.Trainer Todd Pletcher said the initial diagnosis is that the juvenile daughter of Saint Ballado died from Colitis X and that an autopsy will be performed. Pletcher said the undefeated winner of both of her career starts had spiked a temperature around 5 p.m. Saturday. After responding favorably to treatment for the fever, the filly's temperature had improved Sunday morning. By noon Sunday, however, her temperature had begun to rise again. The filly was taken to the clinic near Saratoga Racecourse operated by Dr. Bill Barnes, with tests showing a low white blood count. The filly appeared to be responding favorably to treatment. By midnight, however, the filly had developed projectile diarrhea, Pletcher said, and she died around 2 a.m. Monday."It took her by storm," Pletcher said. "I thought we were being extremely cautious when we took her to the clinic. But that's why they call it Colitis X. They don't know what causes it or how to stop it. That is the fastest I have ever had one go."The death of Freedom's Daughter was the second major setback for Pletcher over the weekend. Left Bank, also trained by Pletcher, underwent surgery Saturday for colic. "It takes the starch out of you," the trainer said.Barnes said Colitis X is a large-bowel disease of the large intestine. He said its cause is unknown but that it is common in horses suffering from Potomac Horse Fever. Padua purchased the filly for $525,000 at last year's Saratoga August yearling sale. She was consigned by Derry Meeting Farm on behalf of her breeder George Strawbridge. In her career debut, Freedom's Daughter broke her maiden by 7 3/4 lengths.