The 16-year-old girl, who cannot be named, faced the Victorian County Court on Tuesday after committing the aggravated carjacking on February 27, two hours after the legislation came into effect.
Under the new laws, children aged 14 and over who commit home invasions or aggravated carjackings will face the county court where penalties are tougher than a children's court.
Judge Scott Johns on Tuesday reminded the parties the case was being heard in the higher court after the girl's lawyer appeared in plain clothes instead of the usual robes.
"We're not the children's court," he said.
The balaclava-clad girl and her male co-offender jumped into the back of the victim's taxi about 2.47am on February 27.
The girl pointed a knife at the driver's neck after he told them to leave, before she demanded he get out of the car and leave his phone and keys behind.
The driver, fearing he would be stabbed, exited the vehicle and called for help as the girl drove the car away with the boy in the front passenger seat.
The pair crashed the taxi a short time later after speeding along the Princes Highway at 180km/h.
The boy was in March sentenced in a children's court to a 12-month good behaviour bond after pleading guilty to carjacking.
But the girl faced the higher court on Tuesday after pleading guilty to the more serious aggravated carjacking charge.
In a statement to the court, the taxi driver said he could no longer work and he had lost his primary source of income.
"I feel scared when a passenger sits in my car," he said.
The girl's lawyer Kate Perry extended a "really deep and sincere apology" to the victim on behalf of her client, who was seated in the front row of the court instead of the dock.
The girl had no prior criminal history but she had a complex background that needed to be considered, the lawyer said.
Ms Perry advised the judge to order a Youth Justice pre-sentence report and direct the girl to undergo a group conference, where she could discuss the offending with the victim and others.
Judge Johns said he was concerned ordering a group conference would "put the cart before the horse" as he still was yet to decide on the sentence.
But the judge said he was happy to adjourn the plea to allow a pre-sentence report to be compiled.
The parties spent the remainder of the hearing discussing which part of the legislation the case could be adjourned under, given it was an underage offender in the adult system.
The hearing was ultimately adjourned to July under a section of the Children, Youth and Families Act.
Judge Johns ordered the girl to participate in the pre-sentence report before the next hearing.
16°C