Melissa Arbuckle had a "significantly disturbed mind" when she killed her three-month-old baby, a court has been told.
The 32-year-old on Tuesday faced the Victorian Supreme Court after pleading guilty to one count of infanticide at Upwey, in Melbourne's east, in July last year.
Defence barrister Megan Tittensor said Ms Arbuckle had been in the depths in of severe postpartum depression and psychosis when she resolved to take both her own life and her baby daughter's life.
The young mother mistakenly believed her child, who would have turned one on Monday, was suffering from shaken baby syndrome and that it was inevitable she would die.
"This act was committed by someone with a significantly disturbed mind," Ms Tittensor told the court.
"She had a fixed delusional belief she had harmed her child and they were both broken.
"She had a perfectionist personality and need for control ... she wanted to be the perfect mother."
Ms Arbuckle doesn't plan on having another child, her barrister said.
"She can't bear the thought of being a risk to another child."
The baby's father, who has requested anonymity, says he struggles with feelings of hatred toward Ms Arbuckle, with whom he is now estranged.
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