Driving west on the 80km/h QEII Drive, near Marshland Rd, McGirr drifted into the east bound lane, until she was completely across the other side of the road.
Tiatoa tried to take evasive action but his Yamaha motorcycle slid into the front of McGirr's Mitsubishi Mirage.
Tiatoa's whānau read emotional victim impact statements to the court this morning.
Tiatoa, described as a responsible and safe rider, was killed just 15 minutes after leaving home for a first date.
The whānau say they initially expressed sympathy with McGirr.
But accusations that Tiatoa had been on the wrong side of the road hurt them. They accused McGirr of "shifting the blame to an innocent man".
It took police five months to charge McGirr.
His mother said she did not want to hear from the driver.
"It means nothing to my family, and whatever you say will give us no closure. You will never bring my son back."
Offers of a restorative justice conference were not taken up by Tiatoa's whānau.
But defence counsel Stephen Hembrow said McGirr accepted responsibility "straight away".
While there were initially allegations that a cellphone may have been involved, the court heard it is now accepted that she was not distracted by the phone.
"She was coming home relatively late, she drifted across the centre line, saw the headlight in front of her… she might have dozed off, whatever. I can't explain it," Hembrow said.
"This is a tragic accident."
McGirr has no criminal convictions, or even any driving tickets, the court heard.
Judge Tom Gilbert accepted her genuine remorse, though described her level of carelessness as being "quite significant", in what was a "dreadful error".
He acknowledged the Tiatoa whānau's loss of "an excellent young man", and that the law's response to their loss may seem "completely inadequate".
Judge Gilbert sentenced McGirr to 120 hours of community work and ordered her to make an emotional harm payment of $10,000 to Tiatoa's mother within 28 days, with the idea of it going to benefit his young daughter. McGirr was also disqualified from driving for 10 months.
