Milka Djurasovic, 40, is facing a judge-alone trial in the Supreme Court of Western Australia charged with two counts of murder.
She has admitted killing her daughters Mia, 10, and six-year-old Tiana, whose bodies were found by their father Nenad at their Madeley home in October 2019, but argues she is not guilty of murder because she was of unsound mind.
Djurasovic was diagnosed after the killings with major depression with psychotic features.
The court heard she had previously struggled with worsening mental health issues and feared her children would be forced into care if she was hospitalised.
An agreed statement of facts submitted to the court outlined how Djurasovic woke around 7am on the day of the killings and thought to herself "today's the day", subsequently placing knives, machetes and rope in the pantry.
Tiana cried when she saw the rope and knives, asking her mother "are you going to do something to me?" and saying she wanted to go to school.
Djurasovic "snapped out of it" and got the girls ready for school, sounding upbeat and normal over the phone when she received a call from her husband.
At the school gates, she parked for several minutes before deciding to return home, telling Tiana they were going to go shopping.
Later that morning she decided to proceed with killing the girls and herself, plugging a vacuum cleaner into the wall and leaving it running to drown out any sound.
After killing her daughters, Djurasovic paced around the home before kissing and hugging the girls and placing toys next to their bodies.
She then made several attempts to take her own life and recorded a video in which she repeatedly apologised and urged her husband to let her die.
The girls' father arrived home that afternoon to discover Mia's body, with Tiana's body later discovered by paramedics.
Police found Djurasovic a short time later covered in a blanket in sand dunes at a nearby beach, having again attempted to end her life.
Several notes which Djurasovic had typed or handwritten were found in the home.
"I love my girls more than anyone and anything and I am so sorry for not looking after them better," she wrote.
"I should have been more 'connected' to my husband and friends. I did not like talking about my problems. I wish I had. I am so sorry for everything."
Djurasovic also wrote to her husband, saying the girls were already nervous and anxious and she didn't want them to "end up on medication, doing drugs and all that is killing me".
"I am at fault for everything," she wrote in the letter, translated from Serbian.
"I did nothing bad on purpose but that is how it ended up."
Psychiatrist Adam Brett, who twice interviewed Djurasovic in custody earlier this year, said he was confident the accused had been mentally impaired at the time of the offending and had lacked the capacity to know she ought not to do such a thing.
He said Djurasovic had nihilistic delusions and believed she was saving the girls from the "awful things" she had experienced.
"She loved them so much she didn't want them to suffer in the same way she did," Dr Brett told the court.
Djurasovic briefly took the stand on Monday to assert, under questioning from her lawyer Mark Trowell QC, that she had been honest throughout her police and psychiatric interviews.
The trial, before Justice Stephen Hall, continues.
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