As the prosecution described the killing, Mrs Thornton broke down in the dock at Oxford Crown Court and sobbed: "Please take me home." The hearing was temporarily adjourned while she recovered her composure.
Mrs Thornton, 41, is on trial for the second time accused of the murder of her husband, Malcolm, at the couple's home in Atherstone, Warwickshire, in 1989.
Mr Justice Scott Baker, the judge, told the jury of eight men and four women, that the retrial had been ordered by the Court of Appeal. He said that they must reach their verdict on the evidence put before them alone.
Brian Escott Cox QC, for the prosecution, said that Mr and Mrs Thornton met in 1987 when he was 42 and she was 10 years younger.
They were both heavy drinkers and alcohol was to play an important part in the case.
He continued: "She possessed a further factor, another degree to the dangerous cocktail of their relationship. This was a personality disorder which was only identified by doctors after the death of her husband.
"The effect of it was to make her compulsively attention-seeking. One of the ways she did that was to shock people by what she said, what she did, how she dressed and how she undressed.
"It is an unhappy aspect of her personality that she frequently tends to tell people what she wants them to hear regardless of the reality. Another cruel way of putting it is that she is, in truth, a pathological liar."
Mrs Thornton was sacked from a tele-sales job for drinking and her husband's alcoholism became steadily worse and he began to hit her. He spent a month in a drying-out clinic, but was back drinking soon afterwards.
In 1989, Mr Thornton lost his licence for drink/driving and had to resign from his job as a security officer. He was arrested for being drunk and disorderly and later punched Mrs Thornton in the face during a row.
Mr Escott Cox said that after one episode of Mr Thornton's heavy drinking his wife was told by Helen Thomas, a workmate, "you have got to sort this out".
Mrs Thornton replied: "The only way to sort this out is to kill him."
On the 13 June, 1989, after spending two nights elsewhere, Mr Thornton returned home and by the evening was sprawled out on the sofa in a drunken stupor. His wife and his son, Martin, who was living with them, decided to go out to a pub.
Before they went out, Mrs Thornton wrote "Bastard Thornton, I hate you," in lipstick on a mirror. When they came back, Martin went to bed.
Mr Escott Cox said that Mrs Thornton had always claimed that she stabbed her husband with a kitchen knife by accident after a row during which he accused her of being a prostitute.
But he said that Martin, who was not fully asleep, "heard a murmured conversation, no raised voices, no shouts".
He then heard someone rummaging through the cutlery drawer in the kitchen.
He said: "Martin heard his father scream and came downstairs to be greeted by Sara saying: 'Martin, I have killed your father.'"
In fact, Mr Thornton died several hours later while in hospital.
The killing, said Mr Escott Cox, was motivated wholly or partly by financial considerations.
He continued: "Sara Thornton had a fixation that if she left Malcolm before she had been married to him for a year she would lose her interest in the house."
Mr Escott Cox said that this may not have actually been the legal situation, but Mrs Thornton thought it was and so killing her husband was "the ultimate solution".
The case continues today.