Leanne Zaloumis, 29, was charged with aggravated burglary after the incident on Saturday night.
Prosecutors said Cowell was watching TV in the bedroom of his London mansion when he heard a loud bang coming from his bathroom and discovered Zaloumis inside with a brick.
Cowell's security staff confined the intruder to a bedroom until police arrived and found her in the wardrobe. Police officers drew their weapons as they arrested Zaloumis, and later found blood stains in the bathroom, prosecutor Paul Mitchell said.
The charge, read out in court, alleges that Zaloumis intended to "inflict grievous bodily harm upon a person therein and at the time of committing the said burglary had with you a weapon of offense, namely a broken house brick."
She also is accused of shouting at Cowell and hurling items at his bathroom window while standing on a roof outside.
Cowell, 52, has gained fame in both Britain and North America as producer and an acerbic judge on TV talent shows including "The X Factor" and "America's Got Talent."
Cowell spokesman Max Clifford said Cowell had described the incident as "just like something out of a horror movie."
"He was shaken up," Clifford said. "Strange as it might seem he feels lucky, because it could have been a gun or a knife in her hand."
Zaloumis, who appeared in court with unkempt hair and a baggy gray sweat shirt, spoke only to confirm her name and address during a brief hearing at West London Magistrates' Court.
District Judge James Henderson ordered her detained until her next hearing on June 12.
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