Maree Crabtree, 51, was arrested on Queensland's Gold Coast on Wednesday morning over the deaths of her daughter (18) and son (26), who were originally thought to have committed suicide until suspicions were later raised.
Their bodies were found, five years apart, in separate houses on Queensland's Gold Coast.
Detectives allege Crabtree fraudulently received over $550,000 from an insurance payment, before allegedly attempting to receive another $125,000 death benefit and $238,000 permanent disability claim.
The police alleged that the killings "haven't been compassionate acts of a stressed [mother] or a mother at her end, we will be alleging these were premeditated direct acts of murder that have been perpetrated on the victims," Australian Broadcasting Corporation (ABC), quoted Detective Inspector Mark Thompson, as saying.
"The deaths themselves, we will be alleging, were financially motivated," he added.