Debbie Inns, 34, of​ Elizabeth Street, ​Port Fairy, pleaded guilty to Warrnambool Magistrates Court to ​driving in a dangerous manner.

She was convicted and fined $800, ordered she do a safe driver course before getting her driver's licence back and banned from driving for six months.

Police said that on November 22 last year the victim driver, her sister and two other passengers were heading west on the Warrnambool-Cobden Road.

The witnesses said a silver Ford Falcon "came from nowhere" heading in the same direction at a speed estimated at 150 km/h.

Inns then followed the victim's car so close that the other diver was concerned there was going to be a collision. 

Near Premier Speedway, on the duel lane Princes Highway, Inns overtook the victim's car, made abusive gestures and then merged quickly into the left lane causing the victim to brake heavily to avoid an accident.

The victim moved into the right lane and Inns swung in front of her, causing the victim to again brake heavily  to avoid a collision.

Defence counsel Adam Bellman said his client had been very keen to get back to Port Fairy to pick up her young son.

He said she was very apologetic that her driving raised such concerns that her behaviour was reported to police.

Magistrate John Lesser said Inns had clearly been involved in a very dangerous driving performance which put other road users and herself at risk.