Her husband's affair and drug addiction had driven her to depression.
In desperation, she tried to reach out to various people, including her husband's mother and close friend, for help.
Even as she was doing this, she was considering a more extreme measure, one that would end in her husband's murder and her own suicide.
Sometime during the night of Nov 4 last year, she burnt charcoal in the bedroom of their Tanglin Halt Road flat.
Her husband had dozed off after taking drugs.
The couple were later found dead in the flat.
A coroner's inquiry ruled that the deaths of Mr Don Lin Jun Yang and Madam Zhang Xiaohui, both 33, were due to carbon monoxide poisoning.
At close to midnight the day before, Madam Zhang, a Chinese national with Singapore permanent residency, had called her Singaporean husband's friend for help after he did not return home for two days.
She also told the friend, Mr Grant Chan Kok Keong, 41, that Mr Lin was having an affair and had taken his mistress to China for a tour.
She wanted him to call the mistress to find out if Mr Lin was with her.
But Mr Chan declined, saying that he did not want to get involved in their marital problems.
The next day at 4pm, Madam Zhang called Mr Chan again, this time using her husband's mobile phone.
He heard her say, "Big brother, Don..." before the line was cut off.
He could hear a commotion in the background during the brief call.
Mr Chan did not call her back as Mr Lin had earlier warned him not to talk to her as she was suffering from depression.
Several hours later, the couple were dead.
It seems that this was not the first time Madam Zhang had tried to harm her husband.
Mr Lin's sister revealed to the police that during his funeral wake, Mr Chan had told her that he was aware of his friend's drug habit and affair.
He also said Mr Lin had complained that Madam Zhang had tried to strangle him and also threatened him with a knife.
Investigations revealed that two friends of Madam Zhang had tried in vain to contact her from about 8pm on Nov 4.
One of them would usually talk or message Madam Zhang every day.
When she didn't hear from her friend for two days, she felt something unusual might happen.
They went to the couple's flat and found the main door locked.
One of them smelled something burning but did not suspect anything.
They found Mr Lin's car in the carpark and called a locksmith to unlock the door at about 3am.
Entering the dark apartment, they saw the couple lying motionless on the bed in their bedroom.
They then called the police.
No physical injuries or strangulation marks were found on the deceased.
The police found Mr Lin holding onto his mobile phone, indicating he might have woken up and tried to call for help but succumbed to the carbon monoxide poisoning before he could do so.
No suicide note was found in the unit or in Mr Lin's mobile phone.
The other bedroom in the three-room flat was rented to a couple, who were in Malaysia at the time of the incident.
One of the tenants said she had been hearing shouts coming from the deceased's room almost every week after midnight since July.
Madam Zhang had confided in friends that her husband had been taking drugs and sought advice on whether to report him to the authorities.
She felt that she would be a cruel wife if she did so.
She also told her mother-in-law, Madam Lee Ah Hock, 58, about her depression over Mr Lin's drug habit and affair.
When Madam Lee said they should talk about this, Madam Zhang said she would drop by on Nov 3.
But she never did.
The investigation report indicated that Mr Lin had been fined $1,000 in 1996 for possessing a controlled drug.
Analysis of Mr Lin's blood revealed small quantities of drugs - amphetamine and methamphetamine - which indicated that he had consumed the drugs some time before his death.
But the drugs had no role in his death, the investigation report said.
Investigations also showed that Madam Zhang had sought medical help for insomnia and for coughing out small amounts of blood a month earlier on Oct 15.
She was very upset
During the second consultation four days later, she told Dr Goh Tiong Jin of My Family Clinic at Tanglin Halt that she was very upset emotionally.
She confided in him that her husband had been having an affair for half a year and had not kept his promise to break off with the other woman.
Madam Zhang admitted to him that she had thought of committing suicide.
Dr Goh prescribed antidepressants and noted that she was clinically depressed.
Investigations also revealed that on Nov 3 at about 12.20pm, Madam Zhang had gone to a Sheng Siong Supermarket outlet and bought three 4kg bags of charcoal and two BBQ nets.
She was alone.
She then went to a shop at Commonwealth Drive and bought two red incense burners.
In her investigation report, Staff Sergeant Marlina Ahmat of Clementi Police Division felt that Madam Zhang was already planning to commit suicide when she did not meet her mother-in-law on Nov 3.
Staff Sgt Marlina said there was no evidence to suggest Mr Lin wanted to kill himself.
And that he was high on drugs when he was murdered by his wife.
She said that while he was asleep, his wife took the opportunity to burn the charcoal and tucked herself into bed under the blanket.
Staff Sgt Marlina felt that Mr Lin might have been sitting on a chair and dozed off.
When he awoke, he probably sensed something was wrong and walked towards the bed to get his mobile phone to seek help.
But by then, it was too late and he slumped onto the bed and died, still holding the phone.
The last call out from his phone was to Mr Chan on Nov 4 at 4pm, which Mr Chan confirmed was made by Madam Zhang.
Outside the court, Mr Lin's sister, Ms Cheryl Lim, 31, declined to comment on the findings and the case.
When asked how her mother is coping, she said: "She doesn't want to remember too much, that's why she wasn't here."
