A 25-year-old domestic maid from Myanmar was sentenced to jail for 13 years yesterday for killing her employer's 87-year-old mother-in-law.

Than Than Win pleaded guilty in the High Court to a charge of culpable homicide for repeatedly stabbing Madam Yong Wan Lan with a pair of scissors at the Springdale Condominium in Hindhede Walk, off Upper Bukit Timah Road, on March 4 last year.

Her charge had been reduced from one of murder as she was diagnosed by a psychiatrist from the Institute of Mental Health to be suffering from severe depression with psychotic symptoms at the time.

In sentencing, Justice Chan Seng Onn told her: "You had viciously and mercilessly attacked and stabbed a very elderly grandmother whom you were supposed to help look after."

The judge noted that she inflicted 21 stab wounds on Madam Yong, two of which were fatal injuries to the heart and lungs.

The depth of the deepest wound, at 11cm, suggested "considerable force" was used, the judge noted.

"There does not appear to be any significant amount of serious scolding or provocation from the grandmother in this case," he added.

The maid had been working for the family of four - her employer, the employer's husband, their daughter and Madam Yong - for more than a year. She shared a bedroom with Madam Yong and would usually be left alone at home with her during the day.

The maid said on the afternoon of the incident, she became increasingly angry over a scolding from Madam Yong that morning.

She got the largest pair of scissors she could find from a kitchen drawer and used it to repeatedly stab Madam Yong, who was too frail to retaliate. After killing her, the maid washed herself in the bathroom with her clothes on. Drenched and barefoot, she left the apartment and wandered around the estate.

She took a saw from a parked truck and tried to cut her neck with it, but was stopped by a worker.

Security guards were alerted, and the police were called. After much persuasion, she told the officers where she lived. She was arrested after the officers found Madam Yong's body in the flat.

Yesterday, the maid's lawyer, Mr Sunil Sudheesan, said that Madam Yong had constantly scolded her for a year. The scolding on the fateful day was minor but, coupled with her depression, it took her "over the edge", he said, asking for less than 10 years in jail.

Deputy Public Prosecutor Isaac Tan sought 12 to 15 years for the "ferocious" attack on a defenceless victim. He argued that even if Madam Yong had scolded the maid, it did not justify a revenge killing.

Than Than Win, who was stony faced on being sentenced, spoke briefly to her father before she was led away. No members of Madam Yong's family were in court.

Culpable homicide carries a sentence of up to 20 years in jail or life imprisonment.