Trudy Collett - better known among racing circles as Trudy Thornton - was sentenced in the Hamilton District Court on Tuesday on a charge of careless driving causing injury.

As she was zooming down Victoria Rd in Cambridge, Trudy Collett heard a thud.

She looked behind her, but could not see anything.

Assuming she had driven over a piece of wood or some other object on the road, she travelled on, turning on to Zig Zag Rd and then heading home.

Warwick Smith/Fairfax nz Lizzie Stannard was sent flying off her bike in the crash, but miraculously escaped serious injury.

But she was mistaken. She had actually struck top triathlete Lizzie Stannard, sending the then-19-year-old flying off her bike. The teenager had landed on her head and was knocked out.

It was a season-destroying injury for the up-and-coming Palmerston North sportswoman, who was later found on the roadside by two women who happened to be nurses, and called for an ambulance.

She suffered lacerations to her ear that required surgery, tissue damage to her neck and back and swelling to her knee. She spent three nights in hospital and for months afterward was unable to work or compete.

By chance Trudy Diane Collett - better known in horse racing circles as Trudy Thornton - is herself a top sportswoman.

The acclaimed jockey has more than 1000 wins to her name and she was the first woman to ride in a Great Northern Steeplechase, in 1986.

The 55-year-old was sentenced in the Hamilton District Court on Monday for what Judge Denise Clark described as "a moment's inattention but with serious consequences" at 5.45pm on Saturday, March 4, 2017, resulting in a charge of careless driving causing injury.

The judge ordered Collett to pay her victim reparation of $1500, and disqualified her from driving for six months.

Clark had earlier presided at a hearing at which an additional charge of failing to stop to ascertain injury was dismissed.

Collett suffered from hearing issues, and was not able to determine which direction certain sounds were coming from, the judge said.

Defendant and victim had been reunited at that hearing and Collett had apologised and had given Stannard a bouquet of flowers.

As defence counsel Thomas Sutcliffe had pointed out, the younger woman had subsequently declined to take part in a restorative justice conference, because she believed Collett had been "through enough already".

Collett had genuinely believed she had not hit anybody. Once she realised she might have been involved in a bad accident the next morning, she returned to the scene of the crash and had then phoned the police.

The consequences of a driving disqualification would not be insignificant for Collett, Sutcliffe said. As a professional jockey she had to drive to various locations around the North Island to attend racing meetings, and not being able to get to those events would deprive her of a good portion of her income.

At the time of the crash, Stannard was in Cambridge visiting a friend and preparing to take part in a triathlon while she was there.

She later told Stuff that she could not remember the crash at all.

"I was riding along Victoria Road coming into Cambridge. I can't remember what happened, but these two ladies rescued me and they ended up being nurses.

She believed herself very fortunate her injuries were not more serious.

"If [the car] was a couple of centimetres to the left I might not have a leg."

Stannard has since recovered from her injuries and has been taking part in competitions in New Zealand and overseas.