Lauren Dickason told police she hadn't felt normal for months before killing her children in Timaru.
A jury at the High Court in Christchurch has watched her police interview, filmed the day after the deaths.
She admits the killings but says it wasn't murder, with a defence of insanity and infanticide.
The Herald's Anna Leask says Dickason told police she'd been "thinking about it... for a while."
"She told the police she'd been diagnosed with a major depressive disorder, however in the month before she came to New Zealand, she'd come off her meds because she was feeling better."
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