A drink driver who badly injured a teenager in a head-on collision was herself hit by a drink driver when she was a child, the Perth Magistrates Court has been told.

Amanda McMahon, 44, was three times over the legal limit when she drove for five kilometres the wrong way on the Kwinana Freeway near the Mount Henry Bridge in May.

Other motorists took evasive action to avoid her vehicle and police were called, but before they had arrived she collided head-on with another car.

Sarah Lavell, 19, a passenger in that vehicle, suffered serious injuries including a fractured spine and pelvic injuries.

The court heard Ms Lavell had only just recently been able to move again without the use of a wheelchair and she was unable to sit, stand or walk properly.

The driver of the car suffered minor injuries.

At a sentencing hearing on Thursday, McMahon's lawyer Lucy Young said her client was "ashamed" and "angry" at herself.

"She was hit by a drink driver when she was 10 and her pelvis was shattered," she said.

"She spent one to two months in hospital... and was then in a wheelchair.

"Because of that she has always been strongly opposed to drink driving.

"She still doesn't understand why she made the decision to drive."

The court heard McMahon had spent the afternoon drinking with friends but was asked to leave their house after she had an argument with her partner.

Ms Young said McMahon had only been in Perth for about a year and she was unfamiliar with the area.

Magistrate Joe Randazzo told McMahon she would receive a jail term when she was sentenced next month.

She was remanded in custody.