"She wasn't responding at all. It certainly didn't look good," she said.
"If she comes through she'll be a very very lucky girl."
The accident, which happened near a bend in the road, comes as the Herald has been highlighting the road safety issues for cyclists and motorists following the death of 37-year-old John Tangiia in central Auckland this month.
The woman who arrived at the scene yesterday said: "She wouldn't have been very far from her own house, maybe one or two neighbours away. She's just a lovely girl."
It was the only time she had seen the girl on her bike without her helmet, she said.
"She didn't have it on and that's very, very, very unusual for her ... She always had the helmet on. Religiously, she wore it."
The woman, who did not want to be named, said she knew the girl and her mother - whom she sat with on the roadside while emergency services helped her daughter.
"She (the mother) was mainly concentrating on her wee girl and telling her to be brave and that sort of thing."
The girl suffered head and leg injuries and was flown in the Westpac rescue helicopter to the Starship hospital, initially in a critical condition, at about 6pm.
Her black and white bike, decorated with a single pink ribbon at the front, remained on the side of the road last night, while the Lexus Sedan - with a caved-in windscreen and substantial damage to the left front - was parked just metres away near some trees.
Senior Constable Steve Carey said the girl had pulled out of the gravel driveway and on to the road in front of the car. He confirmed she had not been wearing a helmet.
The Herald Cycle Safe series has highlighted the issues surrounding safety for cyclists and motorists and generated discussion over issues such as reduced speed limits in residential and shopping areas, cycle lanes, and other changes to make cycling safer.
Eight cyclists died in New Zealand road crashes last year, with the same number in 2012.
Accidents this month
• January 8: John Tangiia died after colliding with a truck in central Auckland
• January 18: Kerikeri maths teacher Bill Bayliss, 54, died after being hit by an SUV
• January 22: Garth Barfoot suffered a broken femur when a car struck him while cycling on Auckland's North Shore