Judge Phillips said Sardana had displayed "the most disturbing attitude and course of behaviour".
"She [the victim] was seen by you as a mark, and you set upon her because you learned very quickly she had savings," he said.
Mr Westgate had argued during the trial that the woman knew the money was for gambling and had taken a risk.
But Judge Phillips said that was false.
"She was not a woman who was going to put her life savings on the line in some form of gambling venture that you supposedly proposed. She thought it was an investment - the keys to the door of economic and commercial success."
The victim was totally ashamed and had to seek help for depression, Judge Phillips said in reference to a victim impact statement.
She felt scared ever since the incident and had lost her ability to trust. That began to return only when she was able to give evidence in court during the trial, the judge said.
Sardana told a probation officer that he regularly spent $1000 a day on gambling and hardly lost.
"For you to say you rarely lose in gambling to me is remarkable and distant from reality," Judge Phillips said.
The curfew for Sardana's community detention is from 7pm to 6am.
Judge Phillips said the victim still lived in Oamaru and Sardana was "well advised to keep well away from her".