She told the Evening Standard: "I 100 per cent thought I was dying. I thought that was it, definitely no doubt in my mind.
"I remember my chest being crushed and taking what I thought was my last breath.
"He stopped just before crushing my head. I was very lucky. I had black eyes for about six weeks from the pressure of the truck being on top of me.'
Heanaghan pedalled off when the lights went green as she turned right from the high street onto Commercial Road.
She was cycling around two metres in front of the truck, but the driver didn't see her, knocking her over and sending her under the wheels.
Her legs and chest were crushed as horrified passers-by shouted at the driver to tell him what happened and get him to stop.
She was attended to by Air Ambulance medics and taken by ambulance to the Royal London Hospital nearby.
After two months there she was transferred for rehabilitation at the Royal National Orthopaedic Hospital in Stanmore, north London.
Heanaghan, of Whitechapel, but originally from Auckland, New Zealand, has won compensation from the lorry driver's company in a civil case represented by London lawyers Fieldfisher.
The Metropolitan police were "incorrectly informed" the accident "was not life-threatening or life-changing" so did not refer the case to its collision department for investigation, Fieldfisher claims.
They were therefore unable to prosecute the driver, but the police witness report did confirm the driver "should have seen" the cyclist.
In their defence statement, the lorry driver said he did not see her in his mirror, as it was only positioned to show the nearside of the HGV.
A spokesman for Fieldfisher said: "Looking to turn right, Sarah overtook the lorry at the traffic lights and believed that she had positioned herself far enough in front of the lorry to be clearly in the eye line of the driver.
"As the driver turned right, however, he pulled ahead of Ms Heanaghan and she and her bicycle were sucked under the wheels of the lorry.
"She remembers feeling as if her hair was being ripped out before she blacked out and woke up in the middle of the road believing she was dying."
Jennifer Buchanan, a personal injury lawyer at Fieldfisher who represented Heanaghan, said that the money secured from the insurers of the vehicle will now pay for the right rehabilitation, accommodation and financial support and will enable her to get back to her family in New Zealand for Christmas.
She added: "In the meantime, however, her life has been ruined.
"Sarah suffers constant physical pain as a result of the accident and battles with depression every day.
"It takes immense resilience and hard work to cope with an accident like this. One minute you're on your way to work, the next your life has been shattered."
MailOnline has contacted the Metropolitan Police and Air Ambulance for comment.
