A 24-year-old woman has been charged with two counts of murder after two bodies were found in a burnt-out shed in Biggenden, north-west of Brisbane, last month.
The fire claimed the lives of the town's baker, 54-year-old Todd Mooney, and his 10-year-old daughter Kirra on December 20.
Twenty-four-year-old Maryborough woman, Kristen Olsen, was also charged with one count of arson.
Her matter was mentioned in the Maroochydore Magistrates Court on Saturday, and she is expected to appear in the Maryborough Magistrates Court on Monday.
Investigators are appealing for anyone who may have seen a white Holden Barina wagon with a distinctive solar panel on the roof driving in the area on December 20 to contact police.
Detective Chief Inspector Gary Pettiford said he could not comment on the woman's motive or what led to the arrest.
"We don't believe that she was known to either of the deceased, or Rebecca, Todd's fiancée," he said.
"We still have a hell of a lot of work to do, and it's all quite sensitive."
The inspector said the woman did have some connections to the Biggenden community.
"She went to school there as a child, so she has lived there in the past, but in recent times she's lived in Maryborough," he said.
Mr Mooney's death came about a week before he was due to marry his partner Rebecca Hansen, who is also Kirra's mother.
The inspector said the three witnesses that came forward had helped with the police investigation.
Authorities were first alerted to the fire on the rural property shortly after midday before six fire crews arrived on the scene.
It took firefighters about seven hours to extinguish the blaze.
Police divers search nearby area
Inspector Pettiford said police divers are searching a body of water in Ban Ban Springs.
"We have found some items of interest but, again, I can't comment on the nature of those items," he said.
"In any search we're looking for something that's not naturally there."
Police are still investigating how the fire was started.
"The building was completely burnt to the ground, which makes our forensic examination quite difficult," he said.
"We do have witnesses who saw the fire in the early stages which has helped but at this stage it's still difficult to determine the origins of the fire."
A team of 22 SES volunteers searched the area in the days that followed the blaze, combing the areas for clues.
Inspector Pettiford said criminal activity in Biggenden is very rare.
"It's a beautiful country township with really law-abiding, community-minded citizens who have certainly helped us with our inquiries," he said.
"They've looked after the police officers that have been out there labouring, and also the family of the deceased."
