"This is a betrayal of trust in respect of somebody vulnerable and trusting," Judge Christopher Field said.
"It causes concern that elderly people can so easily be the victim of scams such as this. The need for deterrence and denunciation is very much a factor in sentencing in your case."
Donnelly's lawyer Adam Couchman told the court she had arranged for a lump sum of $20,000 to be repaid to the victim.
He asked that no further reparation order be made because of the woman's limited financial means.
But Judge Field consigned Donnelly to another $4000 and nearly four more years of paying it off at $20 a week.
He also sentenced her to seven months home detention and 150 hours community work.