"Blackmail is an insidious and abhorrent crime," Judge Michael Turner said.
"If you genuinely thought your sister had been unlawfully taken advantage of, then you would have gone to the police.
"But you saw this as an opportunity to extort money from a visitor to this country."
Judge Turner said he considered imposing a sentence of 17 months' imprisonment, from a starting point of two years.
But he commuted that sentence to nine months' home detention.
Prosecutor Michael Morris had called for a starting point of two and a-half years' imprisonment as "denunciation and deterrent".
Defence counsel Mike Newell said Walker was "a relatively unsophisticated person".
"She has two young children and lives in very modest accommodation. She's very remorseful."
In his victim impact statement, the taxi driver said he lost his job as a result of the allegations and had to return to his home country.
Walker pleaded guilty and was convicted on January 31.