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The Christchurch Polytechnic Students' Association has lost $125,000 after the jailing of the office manager who worked for it for 18 years.

Helen Frances Lenihan, 55, spent about five years over-paying her own wages, paying personal rent, and writing cheques for her own accounts.

The losses totalled $175,000 when the association found out.

Lenihan repaid $50,000 by raising the mortgage on her home. It is now up for sale but there is no prospect of more money becoming available from the proceeds.

Christchurch District Court Judge Gary MacAskill said it was futile to make a reparation order against Lenihan and if the students' association disagreed it could make a civil claim against her.

The woman was in tears as she was led to the cells to begin the one year ten month jail term imposed today. Her family members were distraught and weeping outside the court room afterwards.

Lenihan has no previous convictions, but defence counsel James Rapley accepted that she had "had a mighty fall from grace".

The offending had arisen out of tragic circumstances, at a low point in her life. Her supporters said they could not believe it.

"It is the worst thing I have ever done in my life," she told the probation officer writing her pre-sentence report.

Mr Rapley urged a home detention sentence, but crown prosecutor Shannon-Leigh Litt said home detention was not an appropriate sentence to denounce the offending.

Judge MacAskill said the report showed Lenihan had no problems with drugs, alcohol, or gambling. The offending had been a response to financial difficulties caused by matrimonial problems.

Lenihan had been aware that she needed help, but did not know where to seek it. She had now been seeing a counsellor since 2006.

"Your offending continued over five years. There were plenty of opportunities for you to consider your position, stop offending, and own up to what you had done."

He said home detention would not have sufficient deterrent effect. He also noted that Lenihan was already isolating herself and "further isolation could aggravate your risk to yourself".

Lenihan had repaid the $50,000 before she was charged, and had pleaded guilty at her first court appearance to the charge of theft by a person in a special relationship.

The offending was premeditated, involved a breach of trust, and led to unrecoverable losses of $125,000.