A woman has been charged for allegedly organising an attack on her partner's brother in Sydney's west after a road rage incident last year.

The brother of the woman's de facto partner was sleeping at his house on Clement Street, Guildford, when four men allegedly broke into his house and bashed him with a baseball bat and paving brick about 9.45pm on December 4.

The man, 21, was severely injured and had cuts and bruises, police said.

The 25-year-old woman, who was arrested at Merrylands police station yesterday, allegedly organised the attack after a road rage incident in Granville on the same day.

Police did not say what happened during the incident.

The woman was charged with one count of special aggravated break-and-enter and refused bail to appear in Fairfield Local Court today.

One of the men who allegedly bashed the brother has been charged by police and is facing court. Police are searching for the other three men.

They appealed for anyone with information to phone Crime Stoppers on 1800 333 000.