Jordana Johnson, 36, her 12-year-old son Jordan Norris and his friend Chazz Mather, 12, were killed in the October 15 blaze that destroyed a two-storey home at Gladstone in central Queensland.
It took crews almost two hours to extinguish the fire, with search efforts for the trio hampered by the house's top storey collapsing.
Contessa Leigh Marie Richardson, 37, was injured while escaping the blaze and has been charged with three counts of murder and two counts of arson.
After a week-long investigation, police said they believed the fire was deliberately lit.
Richardson faced a brief bedside hearing in hospital on Friday and was remanded to appear in the Brisbane Magistrates Court on November 24.
"Any investigation that involves a fire, unfortunately, leaves very little evidence for us to go on," acting Detective Inspector Brett Richard said after the woman was charged.
He was tight-lipped about any potential motive for the alleged crimes and refused to comment on the possibility the dead trio had been locked inside the home.
"I'm not at liberty to say the specifics of the events ... however, there is sufficient evidence to commence proceedings," Det Insp Richard said.
Family and friends have been rocked by the charges, he said.
"It has been a shock to them and also the community of Toolooa. Everyone has taken it very hard."
Gladstone state MP Glenn Butcher called for privacy for those impacted by the tragedy so loved ones could grieve.
"I understand charges have now been laid and it's important that we allow the court process to take place," he told AAP.
"This ordeal will never be over for the families after such a tragedy, but I know the Gladstone community will come together to grieve and to support them and each other."
Devastated family members spoke publicly for the first time earlier in the week, remembering the "three beautiful souls" who were "tragically taken from us".
"The impact of this horrific event is being deeply felt not only by our family but by the Gladstone community and across the nation," they said in a statement.
"Our lives, and all those that loved and knew Jordana, Jordan and Chazz are forever changed."
The community has rallied around the victims' families, with a gathering planned at nearby Barney Point Beach on Saturday.
Ms Johnson has been remembered as a devoted mum with a big heart whose children were her world.
Her son Jordan was "fun, playful and cheeky" and protective of his family and friends.
His mate Chazz was described as an outgoing "loving soul with a cheeky attitude".
Chazz was believed to be visiting for a sleepover.
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