While Johnstone lay seriously injured in her vehicle, three people stole her wallet and phone and then went on a spending spree. They spent more than $600, emptying her account.
From her hospital bed, Johnstone told Fairfax the robbery had financially crippled her.
"It was a very, very callous thing to do."
She said she had needed extensive reconstructive surgery on her arm, which was crushed and cut open, and would also need extensive physiotherapy to regain movement.
"They put in a fake elbow. I have a plastic elbow," she said.
Johnstone said she had woken up with no memory of the incident.
Police confirmed the "callous act" and say they are following strong lines of inquiry.
"The offenders' actions by preying on someone involved in a serious crash has only added to her trauma," a police spokesperson said.
Shortly after the incident Howell took to Facebook and vowed to track down the "low-life piece of scum".
The robbery was "totally beyond belief", Howell wrote in an emotional post, which has been shared more than 10,000 times.
"We are on a very busy road at a major accident and even with her bleeding out and semi-conscious this piece of trash thinks it's okay to rip her off!"
He managed to track Johnstone's iPhone, which had been thrown into a hedge of the medical centre opposite the Z station on Clevedon Rd.
It had about 30 missed calls from Howell on it, as he had been waiting for Johnstone to pick him up, Howell posted.
Police said they were called to a crash involving a car and a small truck at 1.15pm on Thursday, November 2.
The 39-year-old driver of the car was seriously injured and had to be removed from her vehicle.
"It has been subsequently established that whilst she was receiving medical attention a person or persons has removed her wallet and phone from her car,'' a police spokesman said.
"A credit card from the wallet was fraudulently used on eight occasions later that day."
Police are appealing to anyone who may have witnessed the incident to contact them immediately.
