Sarah Ashlee Good, 20, pleaded guilty to seven counts of damaging property after 71 charges were withdrawn.

Co-accused Kaileb Lamelza admitted to damaging 25 vehicles by leaning out of the window Good was driving and smashing them with a hockey stick, thinking it would be "fun".

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An agreed set of facts tendered to court said that on July 16 last year, Lake Illawarra police started receiving an unusually high number of reports of malicious damage to cars parked on residential streets in different suburbs.

Police alleged Good and Lamelza damaged 22 vehicles around the Oak Flats and Barrack Heights area that day, then on July 24 and 25, allegedly smashed 22 more vehicles in Kiama, Shell Cove and Jamberoo.

Police alleged 16 more vehicles were smashed in the Nowra area on the same night.

CCTV footage depicting a suspicious vehicle, a Mitsubishi Lancer, with a broken rear right light and distinctive sticker on the bottom right corner of the rear window was obtained and distributed to police patrols.

On July 29 at about 1.30am, police were patrolling the Barrack Heights area after receiving more reports of damaged vehicles when they stopped a Mitsubishi Lancer, driven by Good, matching the description of the suspicious car.

Police found Lamelza in the rear seat, with a wooden hockey stick next to him and broken glass in the footwell.

They were arrested and taken to Lake Illawarra Police Station, where Lamelza admitted to damaging vehicles by leaning out of the window and hitting them with the hockey stick.

The damage included broken rear windows, side mirrors and windscreens, as well as scratched panels, but no property was stolen.

The agreed facts said Good did not "show any remorse" for her actions.

She will be sentenced on March 26.

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