A woman, whose husband raped her teenage niece, told the girl not to tell the doctor that she had consumed bleach because she was distraught over the sex attack.

This was to prevent the husband's crime from coming to light, a District Court heard yesterday.

The 47-year-old woman - the girl's paternal aunt - was sentenced to six months in jail after pleading guilty to perverting the course of justice.

Another charge of failing to report to the police when she had reason to believe her husband had committed rape was considered during her sentencing.

Her 55-year-old husband is now serving a 20-year jail term for raping the girl and other offences.

Deputy Public Prosecutor Michael Quilindo said the woman was asleep in the master bedroom of the flat in Woodlands on the afternoon of Dec 20, 2012, when her husband raped the then-14-year-old girl in the living room.

Distraught over the sexual assault, the teenager drank a solution of water, bleach and soap powder and began vomiting.

The woman - who is not named so as not to identify her niece - heard her being violently sick and found out from her husband what had happened.

As the girl was very distressed, the woman realised that her niece had not consented to sex.

The man dissuaded the woman from taking the girl to hospital, saying it would result in a police report.

The woman took the girl to a private clinic and told her not to tell the doctor what she drank.

A few days later, she gave her niece $50, claiming that it had been given to her by a relative. She asked for another chance to "protect her".

However, the offences came to light in January 2013, when the girl's school counsellor queried her on her lengthy absence from school.

Pleading for leniency, the woman's lawyer Rajan Supramaniam said his client regretted her foolishness and extended her sincere apologies to the victim and her family.

DPP Sharmila Sripathy-Shanaz said the adult who ought to have protected the girl chose instead to silence her.

If the deception had continued, the victim would have continued living with her tormentor.

"Victims of familial sexual abuse invariably feel additional pressure from family members not to expose the rapist, out of a misguided reaction to preserve the unity of the family," she added.

District Judge Crystal Ong said this was a very serious offence of rape. It took place within the family, which made it even harder to detect, and allowed the accused to abuse her relationship with the victim to obtain her silence.

The maximum punishment for the offence is seven years in jail and a fine.