When Ms Clarke spoke to police for the first time about estranged husband Rowan Baxter on December 6, 2019, she was unaware she was in a domestic violence relationship, Senior Constable Kirsten Kent told the inquest.
It is examining the 2020 deaths of Ms Clarke, her children - Aaliyah, six, Laianah, four, and Trey, three - and Baxter, who torched the family in a car on a suburban Brisbane street.
Ms Clarke did not want to take further action at the time, but Snr Const Kent was concerned when told Baxter made the 31-year-old have sex every night.
"She said it's like a chore that she has to do at the end of the day," the officer said.
Seeing Snr Const Kent days later at the Carindale Shopping Centre sports shoe store where she worked, Ms Clarke was immediately "so fearful" thinking something had happened to the children who were with Baxter.
"Her level of fear was like, I have not seen such authentic fear from an aggrieved (person) before," Snr Const Kent told the Coroners Court in Brisbane on Monday.
A police protection notice was put in place against Baxter on December 29, beginning the process of getting a permanent domestic violence order which Snr Const Kent knew was going to be "an uphill battle".
"I just knew he'd fight it," she said.
"I'd started to build up a bit of a picture of what type of man he was."
Baxter breached a temporary order on January 31, when he grabbed Ms Clarke's wrist during an altercation while dropping their son off at Ms Clarke's parents' home.
In audio played in the court, Baxter portrays himself as a victim, telling the officers who spoke to him about the breach: "I've done nothing wrong."
The breach frightened Ms Clarke more than she let on, according to text messages read to the inquest.
"I know given the opportunity he wouldn't hesitate to kill me, I can see the look in his eyes," Ms Clarke wrote to Snr Const Kent.
Ms Clarke also told the officer that Baxter was "so not right in the head".
"The way he would put me in the choker hold showing me his jujitsu stuff was f***ing scary," she wrote.
"I'm strong, but not strong enough to get out of that."
In response to Ms Clarke fearing for her life, Snr Const Kent said: "Don't think like that, you have to be aware but not terrified."
Asked whether she appreciated how serious Ms Clarke's situation was, the officer told the inquest: "I'm still not sure what further action I could have done at that point."
Snr Const Kent also took a statement from Ms Clarke's best friend Nicole Brooks while compiling evidence for the domestic violence order.
Ms Brooks told the inquest last week she went to police on February 13 because of fears for Ms Clarke's safety.
"I said, 'I'm sure he's going to take them out'", Ms Brooks told the inquest.
But officers said they couldn't do anything until Baxter "does something".
"I said, 'what if you don't get a second chance?'"
Snr Const Kent said Ms Brooks gave a statement for the domestic violence proceedings at the officer's request.
"She did express deep concern for them all which I shared," the officer told the inquest.
Snr Const Kent said police do not put people in jail because a best friend comes to the station saying she was worried.
"We don't have a just-in-case prison," she said.
Instead the officer was trying to make sure they got the domestic violence order.
Ms Clarke was leaving her parents' home in Camp Hill to take her children to school when Baxter got into the car, poured fuel inside and set it alight on February 19, 2020.
Baxter, 42, then stabbed himself with a knife, dying nearby.
Ms Clarke died later the same day in hospital.
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