Mum to fight charge she murdered children

The lawyer for a woman charged with the "calculated" murder of her two adult children says her client will "vigorously" fight the charges.

Maree Crabtree was arrested and charged with the deaths of her 26-year-old son Jonathan and 18-year-old daughter Erin, five years apart, on Wednesday morning following a complex police investigation that also spanned other states.

The 51-year-old, arrested in the south Brisbane suburb of Coorparoo, was also charged with the grievous bodily harm and torture of a 25-year-old woman, and several fraud offences.

Her lawyer Emily Lewsy told reporters outside the court on Wednesday Crabtree would "vigorously defend the charges."

Detective Inspector Mark Thompson said police alleged the murders were "premeditated" and financially motivated.

"These acts haven't been compassionate acts of a stressed mother at her end," he said after her arrest.

"It was calculated, it was planned and it was executed with an end goal in mind."

Crabtree was remanded in custody and her matter is set to return to court on February 12.