Nicki Allwright, 19, was killed when her Mitsubishi sedan struck a tree on Gawler-One Tree Hill Road at Yattalunga, in Adelaide's north, on Friday morning.

Ms Allwright, from Craigmore in Adelaide, was driving to work just before 7am when the accident occurred.

The car crossed to the wrong side of the road, before coming back to the correct side and crashing into a tree, police said.

Ms Allwright died at the scene.

A duck was found lying on the road about 100 metres from the scene of the crash.

Online tributes are pouring in for the teenager, who had been looking forward to a holiday in Bali; she and her family were due to leave just two days after she died.

Ms Allwright's mother, Marion, told The Advertiser in Adelaide that her daughter, who had been studying human movement at the University of South Australia, had been eagerly anticipating the holiday.

"We've had a countdown going - 100 days, 80 days, 60 days and the last fortnight she was so excited, saying, 'Bali, Bali' all the time," Mrs Allwright told the newspaper.

"It's all the silly things you plan, like we were going to do the weeding and housework on Saturday so the house was ready.

"She had organised for her friend to come and house sit. And unfortunately it was her best friend's birthday on Friday - the day she died."

Ms Allwright's siblings - her brother Joel, who plays soccer for Adelaide City FC, and sister Samantha - posted photographs of their sister on Facebook.

Many people left messages on the photos.

"Your gorgeous little sister [was] a very welcome visitor at our house. Always with a smile on her face - gentle and kind, but gone too soon," wrote one person.

Another said: "We are all in shock and disbelief, beautiful smiley Nicki. Sending you, Sam, your mum, dad and the whole family so much love xx"

Marion told The Advertiser that she and her husband, Alan, had previously warned their three children not to use Gawler-One Tree Hill Road because it was dangerous.

The road has a 100km/h speed limit, but the Allwrights believe that should be lowered to 80km/h.

"Alan would always tell them, 'Don't go that way, use Main North Road, I hate that road,' " Marion said.

"She just swerved to miss a duck - it was reflex."

The NRMA says insurance data shows kangaroos are the animals most likely to be involved in a road crash in NSW, followed by dogs, cats, wombats and cattle.

The motoring organisation advised drivers who see an animal on or near a road to try to brake, but not to swerve to avoid a collision.

Fairfax Media