The wife of Sydney's most colourful deputy mayor is accustomed to appearing in a supporting role outside court. Now Aysha Mehajer is fronting her own legal battle.

The 29-year-old former beautician will pit herself against the NSW Police when she challenges a defective vehicle notice issued when she was behind the wheel of a "brand new" $250,000 Mercedes G63.

Ms Mehajer was pulled over in October last year and "told to walk home" after police claimed the car's side exhaust did not comply with Australian standards, her husband and Auburn deputy mayor Salim Mehajer said at the time.