"I just told the police because I want to know who murdered that girl," the woman told One News.
"To have my son involved. To have that young girl that's gone, we need closure."
Police did ask her last year about items found with Katrina's body, including a tarpaulin and yellow raincoat the woman remembered being in her mum's garage.
However, the woman said she'd never given a formal statement.
Until last year, the woman had never heard of Katrina Jefferies, she said.
Police issued a statement saying their investigation was ongoing and would soon be subject to an internal peer review.
"The review of historic unsolved cases is a standard police practice that allows for reassessment of further investigative and evidential opportunities," said the statement, released to One News.
"We remain committed to bringing the person[s] responsible to justice. We are mindful however that this remains an open and ongoing investigation, and because of this, will not be drawn on further aspects at this time."