Nicole had been in the back seat of the car, travelling with three other people. Trudi said witnesses had seen people fighting in the car shortly before Nicole fell out, though police would not comment on this.
"They weren't sure if she jumped to get away from them or she was pushed," she said.
When she saw her daughter in hospital, Trudi said there did not to be any injuries consistent with jumping from the car - just full impact to her head.
"I queried that if she jumped, how come she hasn't got hurt ankles?
"That's something that no one commented on."
Detective Senior Sergeant Greg Cottam said the case would stay open, at least until the coroner releases a finding on how Nicole came to fall from the vehicle.
He said the death was treated as "unexplained" and the case would remain open "until such time as it's been resolved".
There was no evidence to support charges being laid.
When asked about reports witnesses saw people fighting in the car before Nicole fell out, Cottam said it would be unfair to witnesses for police to comment on what they have or haven't said, before the coroner's decision was released.
"I do know that there has been a lot of rumour and innuendo around this whole thing, which has made it difficult, but it has been a very thorough investigation and a lot of witnesses have been spoken to."
He said witnesses had given police "quite a good picture of what has happened" but it was not up to police to determine the circumstances of the fall.
"Police understand how hard it is for the family of Nicole. They're searching for answers. We have met with the family and outlined the findings from our investigation.
"The circumstances around this are tragic ... our sympathy goes to the family of Nicole, who are struggling to come to terms."
Trudi said her daughter became addicted to drugs "towards the end" of her life, but was always a well-liked, clever and colourful person.
"Even in her struggling times you could hear when she was coming to visit, because she was always laughing.
"Her personality was bigger than herself - because she was a little dot.
"I don't want her to be forgotten, that's my struggle. If she was pushed out of that car, I want someone to answer for that."
Trudi had been told her daughter was in some type of trouble in the days leading up to her death. She received a call from someone concerned about the people Nicole was with.
"I phoned her at midnight ... I said, 'Where are you Nicole?' She said, 'I'm okay'."
The pair arranged to meet on the Saturday, but later on in the day of their phone call, Nicole suffered what would be fatal injuries.
"I feel more sorry for her than anyone else. She fought really, really hard for three weeks to live. She really fought.
"Most days I just think, 'Oh, Cole, what a shame that you're not here', because she loved life."
Now, the lack of answers and the mystery of what happened leaves "a very big, open wound" for Trudi.
"I still sometimes wait for her to come home, that's for sure. I know she's not, but I certainly have some times where I think, 'Wow, this is it now, forever. I'm not going to see you.'"