The Kiwi mother of Australian girl Tiahleigh Palmer has today addressed media for the first time.

Cindy Palmer spoke of her heartbreak and disgust at learning her daughter's foster brother and father are accused of killing the 12-year-old.

Tiahleigh's foster father Rick Thorburn is charged with her murder and his son, Trent, 19, has been accused of incest.

Palmer remained composed throughout the press conference at a Queensland police station, that was live streamed online.

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She thanked police, the media and the public for their support, but asked that people now respected her and her family's privacy.

"Her three siblings will grow up without their sisters ... I feel like a piece of my heart is missing," she said.

"I will not let Tiahleigh's death be in vain, the time has come to get justice for Tiahleigh."

Detective Superintendent Kerry Johnson answered questions from the media before Palmer spoke.

Johnson said the mother was unaware of an alleged incestuous relationship between her daughter and her foster brother, Trent.

He said that police had contacted Facebook to access deleted conversations that helped them form their case. Officers were still looking for evidence in the case, he said.

Rick Thorburn was yet to speak to police, he said.