Paramedics treated her at the scene and rushed her to hospital but she died of a heart attack on the way.
Chilling images from the waterpark allegedly show the hole Araujo slipped through before tumbling to her death.
Fireman lieutenant Eurico Fernando said the launch platform for the zipline had not even been signed off by an engineer.
"It was assembled at the last minute, it was ready on the morning of the 2nd", the same day she died, he said.
"They did it very quickly, possibly this rush in the assembly of this structure is a preponderant factor in trying to explain what happened."
The park did not respond to the allegation.
In a statement, the water park wrote: "Piracema Park Club provided all support and attention to the young woman's family and, after the accident, closed the activities of the attraction ...
"Which will only return to operation after investigation by the relevant authorities regarding the causes of the accident."
The case has been reported to the police and is under investigation.