Latisha May McNally and her passenger, who was hitch-hiking, both suffered fractured skulls as a result of the accident.
Deputy High Bailiff Rachael Braidwood also banned McNally from driving for 18 months.
The court heard that McNally had been attempting to overtake vehicles at excessive speed on the Mountain Road near the 33rd milestone, on June 3 last year, when she lost control of her Porsche.
She was initially charged with causing serious injury by dangerous driving, but that charge was later reduced to one of causing serious injury by careless driving.
McNally, who lives at Slieau Curn Park in Kirk Michael, was represented in court by advocate Stephen Wood.
Mr Wood submitted nine letters of reference for his client, saying that it was apparent that she did a lot of good work in the community.
The advocate said that, at the time of the offence, the Mountain Road had been one-way only and it had taken place in a de-restricted zone.
Mr Wood said that, due to the injury McNally had suffered, she did not have a clear recollection of what happened, but had been air-lifted to hospital herself.
Her passenger had said that he had been hitch-hiking to get back to his campsite in Douglas, after spending the night in Ramsey.
Mr Wood said that McNally was a self-employed builder who was undertaking her own project, which required her to move materials around, so the inevitable driving ban would significantly impact her.
The advocate said that his client had been on her way to undertake voluntary work at the time of the accident and had been wearing her St John Ambulance uniform.
Mr Wood said that it had not been a prolonged period of poor driving.
A probation report assessed McNally as a low risk of reoffending and low risk of harm to others.
Deputy High Bailiff Ms Braidwood told the defendant that she considered it a ‘high end due care’ offence.
She said: ‘You were attempting overtakes at excessive speed, ultimately resulting in a catastrophic road collision.
‘It is fortunate that you were both not killed and also fortunate that another vehicle was not involved.’
McNally was also ordered to take an extended driving test at the end of her ban and to pay prosecution costs of £54.
She agreed to pay the fine and costs within seven days.