SINGAPORE - A couple who cruelly abused their 26-year-old flatmate for eight months until she died from a horrific beating in April 2015, were sentenced to jail on Friday (Dec 1).

Tan Hui Zhen, 33, was sentenced to 16½ years' jail, and her husband Pua Hak Chuan, 38, was given 14 years' jail and 14 strokes of the cane.

The couple had pleaded guilty on Monday to various charges for the extensive torture of Ms Annie Ee Yu Lian, a waitress who had intellectual disabilities. She died from multiple injuries in their Woodlands four-room flat.

Justice Hoo Sheau Peng said on Friday that this was an "appalling" case and that the couple had abused the victim in an "extremely cruel and inhumane manner", causing her to die an undignified death.

They were initially charged with murder. The Straits Times understands that the charges were amended after police completed investigations into Ms Ee's death and on the basis of forensic pathologist reports.

Tan pleaded guilty to two counts each of causing grievous hurt and causing grievous hurt with a weapon, while Pua pleaded guilty to one count of causing hurt and two counts of causing grievous hurt with a weapon.

Justice Hoo said Tan and Pua had abused the trust of a vulnerable victim who treated them as her family. When Ms Ee suffered in silence, this emboldened the couple to escalate the violence inflicted on her, said the judge.

Tan suffered from depression and borderline personality disorder, but the judge said she gave this little weight. However, the judge took into account as a mitigating factor that the couple had come clean in revealing what they had done to the victim.

Ms Ee first met Tan when they were teenagers. They rekindled their friendship in 2013.

Estranged from her family, Ms Ee moved into Tan and Pua's flat in late 2013 and was tasked to do the housework.

She called Tan "jie jie" ("older sister" in Mandarin) and Pua "jie fu" ("brother-in-law").

But she suffered horrendous abuse at the hands of the couple she considered her family.

Tan started assaulting Ms Ee in August 2014 after she blamed the victim for a bedbug infestation. Tan slapped and whipped her, tried to strangle her, banged her head against a wall, and kicked and stepped on her.

Pua was the "standby slapper" who occasionally took over when Tan became tired.

Ms Ee suffered in silence as Tan punished her for misdeeds such as lying or taking too long in the shower. The beatings progressively became more frequent.

In March 2015, the couple started to assault her with a 1kg roll of shrink wrap, targeting her buttocks, where the injuries would be less conspicuous.

Almost daily, the couple beat her with the roll of wrap, making her verbalise her "mistakes" and declare that she would "change". The beating sessions went on for as long as two hours.

The repeated assaults left blisters on Ms Ee's buttocks that were so serious that the couple had to use sanitary pads to dry and bandage the wounds.

On the morning of the fatal assault on April 12, 2015, Ms Ee cut her wrist with a pair of scissors but Tan took the tool away.

By then, Ms Ee was weak with multiple rib fractures, was covered in bruises and blisters, and was short of breath and incontinent.

But later that day, on seeing her lying in her own urine, the couple accused her of urinating on the floor to get attention. While she lay slumped in a chair from exhaustion as they scolded her, they decided to punish her for her "bad attitude".

Tan forcefully swung the shrink wrap against Ms Ee's back multiple times as the victim pleaded with her to stop. When told to return to her room, she lost her balance and fell to the floor.

Pua told the victim to "stop acting" before thrusting the shrink wrap at her abdomen as she curled her body up. Not satisfied, he smashed a dustbin down on her with such force that the plastic bin cracked.

The next morning, after discovering that she was dead, Pua tore off a layer of plastic from the shrink wrap and flushed it down the toilet to get rid of fingerprints.

Tan then called her own brother to say Ms Ee had committed suicide, but eventually called the police.

When the officers arrived, Tan said the victim was a clumsy person who would often injure herself. She also claimed that Ms Ee often jumped up and landed on her buttocks for no apparent reason.

The couple later admitted assaulting her.

The couple also subjected her to psychological abuse by undermining her sense of self-worth and calling her names.

They also exploited her financially by making her surrender her salary of $1,200, from which she was given a weekly allowance of $50, which was later cut to $30.

An autopsy report showed that Ms Ee suffered fractures to seven vertebrae and 12 ribs.

She died from a rare cause known as acute fat embolism.

This occurred when, as a result of the blunt force impact on her buttocks, fatty tissue entered her bloodstream and travelled to her lungs, creating a blockage of the blood vessels.

This interfered with blood getting oxygen in the lungs, leading to progressive cardiac and respiratory failure.

Speaking to reporters outside the courtroom, Tan's eldest brother apologised to the victim's family. He agreed that the couple should be firmly punished for what they did and that he hoped "it will be a lesson for everyone".

He also dispelled public speculation that the couple were facing less severe charges as a result of family background or money, noting that lawyer Josephus Tan from Invictus Law Corporation was acting for them on a pro bono basis.

Pua's mother, through Mr Tan, said she was deeply apologetic to the victim's family and that her son got what he deserved. She also asked for the public's understanding and forgiveness.