Leanne Zaloumis pleaded guilty to one count of intent to damage or destroy property during a hearing at Isleworth Crown Court on Friday (July 6).
However, the 30-year-old from Catford in South East London denied two further charges of affray and burglary.
The court was told that Cowell heard a loud noise while watching television in his bedroom on March 24, the day of the alleged incident.
[Simon Cowell's West London home]
Judge John Denniss did not sentence Zaloumis at today's hearing as a result of administrative delays, but she was informed that she will be sentenced on August 2.
She was granted bail on the condition that she wears an electronic tag, stays at her home address, and is subject to curfew between 19.00 and 07.00.
Zaloumis, who has already spent three months in custody, was also told by the judge that she is not allowed to go within 300 yards of Cowell's home and must not attempt to contact him.