Wendie-Sue Dent denied killing her de facto husband David Lawrence at the Adelaide home they shared in December 2015 to claim his $400,000 estate.
She had been named the beneficiary of his $175,000 superannuation fund and also stood to inherit the home valued at $235,000.
Dent was originally convicted by a jury in April 2020, but later had that verdict overturned on appeal.
After a second trial by judge alone, Supreme Court Justice Sophie David on Thursday again found her guilty.
Justice David said prosecutors had argued that Dent told many lies in the days and months following the death of Mr Lawrence, out of a consciousness of guilt to lay a false trail.
Defence counsel said there was no direct evidence that Dent administered the fatal drugs and it remained possible that Mr Lawrence had self-administered for pain relief.
"Notwithstanding defence counsel's arguments, I am satisfied beyond reasonable doubt that Ms Dent administered the prescription drugs to the deceased," the judge said.
"I am satisfied beyond reasonable doubt that this act or acts caused the death of the deceased, that her act or acts causing the deceased's death were without any lawful excuse or justification and that at the time she administered the drugs causing the deceased's death, she had a specific intention to kill him."
Under SA's sentencing laws, Dent will be jailed for life, but submissions in relation to a non-parole period will be heard at a later date.
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