Leanne Zaloumis was arrested March 24 at Cowell's west London mansion.
Prosecutors say Cowell was watching TV in his bedroom when he heard a loud bang coming from his bathroom and discovered Zaloumis inside with a brick.
At a court hearing Friday, Zaloumis admitted possessing a brick with intent to damage or destroy property, but denied burglary and affray.
Judge John Denniss said the 102 days Zaloumis has spent in jail were sufficient punishment, but warned she would go to prison if she breached her bail conditions, which forbid her from contacting Cowell or going within 300 yards (meters) of his home.
