Lisa Lines, 43, was taken into custody at Brisbane Airport by Queensland homicide detectives on Thursday upon her arrival in Australia.
The historian - a respected expert on the Spanish Civil War - was arrested in the island nation of Palau earlier this month.
The arrest relates to a convoluted series of events that began with a violent incident in the Adelaide Hills in October 2017.
Lines' former partner, Jonathan Hawtin, was rendered tetraplegic - paralysed from the neck down - after being struck repeatedly in the neck with a hatchet by her then-partner Zacharia Bruckner, who was shot in the abdomen.
Mr Hawtin, 36, was charged with attempted murder for shooting Bruckner, 30, with police assuming the younger man was acting in self-defence.
However, a jury of six men and six women unanimously acquitted Mr Hawtin in 2019 after three hours of deliberation.
Lines had in June 2017 told Mr Hawtin, with whom she had two children, that she wanted to separate, the jury was told.
She began a romantic relationship with Bruckner in August that year.
The court was also told Lines had a relationship with another woman and the pair discussed suffocating Mr Hawtin as he convalesced in hospital.
The other woman was spotted at his rehabilitation centre on New Year's Day 2018, the jury heard.
In 2020, major crime detectives in South Australia reopened the investigation, resulting in a warrant being issued for Lines' arrest.
Bruckner was arrested in Brisbane earlier in November on conspiracy to murder offences and extradited to SA.
The pair are accused of attempting to murder Mr Hawtin in the October 2017 incident, as well as co-conspiring to murder Mr Hawtin and his mother Rhonda Hawtin between December 2021 and August last year.
Lines is also charged, along with the other woman, with attempting to murder Mr Hawtin on New Year's Day 2018.
Lines was remanded in custody at the Brisbane City Watch House.
She is due to appear at the Brisbane Magistrates Court on Friday where detectives will seek her extradition to South Australia.
Police have refused to rule out further arrests and charges in relation to the matter.
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