Alesha Ahmed's arrest ultimately led to the conviction of her parents, Iftikhar and Farzana, for murdering their eldest daughter.
While being interviewed about the robbery, Alesha, now 24, revealed to detectives for the first time that she and her siblings witnessed Shafilea's murder seven years earlier.
Shafilea, 17, vanished in August 2003 and her decomposed remains were discovered in Cumbria in February 2004 but it was Alesha's statement to police that provided enough evidence to charge the parents, leading to their convictions this year.
She was sentenced to a 12-month prison sentence, suspended for two years, at Southwark Crown Court, in London, today after previously pleading guilty to robbery.
She helped organise the crime at her parents' home in Warrington in August 2010.
Sentencing the 24-year-old, who is in a witness protection scheme, Mr Justice Irwin said: "In my view, this is a case for mercy.
"I bear in mind all of the extraordinary circumstances I have outlined, in particular the truly appalling nature of what you had to witness, the impact this has had on you, and what you went through to be a witness.
"I bear in mind that, despite your undoubted intelligence and despite the help you may be given, your future life will be overshadowed by all that has happened, and it may be a long time before you achieve peace of mind and anything like normality."
He told Ahmed: "Yours is an extraordinary and terrifying story."
He said robbery in the home was a very serious crime and she would have realised it would be a terrifying experience and said the normal sentence for an offence of this kind would be a significant jail sentence, even for someone of good character who pleaded guilty.
But he said that although Ahmed's role in the robbery was "crucial", there was a "degree of unreality" about how she behaved.
He said she had been in witness protection for more than two years, adding: "This can properly be compared to house arrest, and I accept it had an especially intense effect on you, since you were psychologically vulnerable, you were in a state of conflict with your family, isolated and away from friends and any ordinary support."
He said Ahmed was not trying to bargain for a lower sentence in giving evidence and had asked to be sentenced before her parents' trial.
Handing her a 12-month prison term, suspended for two years, the judge said she would be supervised by the probation service and will also have to undergo continuing mental health treatment, adding: "I am confident you will not re-offend."
During her parents' trial at Chester Crown Court, Ahmed told the jury they pushed Shafilea on to the settee in their house and she heard her mother say "Just finish it here" as they forced a plastic bag into the teenager's mouth and killed her in front of their other children.
The prosecution said the couple killed their "Westernised" daughter because they thought her behaviour was bringing shame on the family.
Taxi driver Iftikhar, 52, and Farzana, 49, denied murder but were convicted by a jury on August 2 this year and both jailed for 25 years.
Farzana Ahmed is currently seeking to overturn her conviction.
Southwark Crown Court heard today that Alesha Ahmed helped organise an armed robbery at the family home in Liverpool Road, Warrington, Cheshire, in August 2010.
Three masked men broke into the house, tying up Farzana Ahmed and three of her children.
They were armed with a gun, a hammer and iron bar and ransacked the property before fleeing with cash and jewellery.
The judge described how Ahmed had been "drawn into" protecting her parents, saying: "You were forced for years to carry this darkest of secrets", and described the violence the couple's children had been subjected to.
Outlining the case, prosecutor Owen Edwards said: "This is a case of truly remarkable background."
He said Farzana Ahmed, son Junayde, daughter Mevish, and a younger daughter who cannot be named, were the victims of a "terrifying armed robbery" by three masked men.
"These men have never been caught but the robbery involved an inside woman - Farzana Ahmed's own daughter Alesha," he said.
"It may never emerge what drove Alesha to participate in this serious crime," he said, but when she was interviewed by police she then told them that she had seen her parents kill her sister.
"Alesha Ahmed provided a witness statement confirming she had witnessed her sister Shafilea being murdered by her parents on September 11 2003.
"Without a shadow of a doubt her participation in the trial of her parents in which she gave evidence over eight days in May 2012 was the key feature in their conviction and also in remedying a near-decade of injustice.
"This is therefore a case in which it can be said that Alesha's evidence was essential in proving the most serious of cases."
The court heard that, in what the prosecution described as either an abortive first attempt at the robbery or to check out the house, Ahmed, who was not living there at the time, visited in the early hours of August 25 2010.
She later left and was seen getting into a car with three Asian men, who she told her mother were trying to get money that she owed them.
That same evening she visited again. After her father went to mosque, she contacted her accomplices and unlocked the door.
The three men broke into the house, armed with a gun, a hammer and a metal bar.
They tied up the family - except Ahmed - threatening to kill them all, the court heard.
"Alesha was never tied up, the robbers referred to Alesha by name," Mr Edwards said, and described how she showed them where her parents' bedroom was.
Junayde Ahmed was kicked as he lay on the ground by a man wearing a steel toe-capped boot, and Mevish was hit in the shoulder with the hammer, the court heard.
Both tried to fight the men, who fled the scene.
One neighbour, whose attention had been drawn by the noise, heard Farzana Ahmed shout at Alesha: "This is down to you, you rotten bitch, you were texting all night and you opened the door to them."
Police who arrived noticed the hostility between her and her family, the court heard, and were worried for her safety.
Her parents claimed the robbers had taken jewellery worth up to £10,000 and £30,000 in cash, but police were sceptical about the amounts they gave, the court heard.
Ahmed was arrested and told police about her sister's murder.
"It was that statement that set in place the turn of events leading to her parents' conviction," Mr Edwards said.
Ahmed originally denied the robbery, until text messages were recovered showing her communicating with the robbers.
She went on to plead guilty, saying she did not know they were planning to use weapons.
Isabella Forshall QC, mitigating, said Ahmed - "a young woman of irreproachable good character" - had wanted to be sentenced before her parents' trial so nobody would think she had made a deal.
She said that, although Ahmed's role in the robbery was significant, there was nothing she could do when the men turned up with weapons.
She told the court: "This particular house was a killing ground of Shafilea and its privacy was a scene and an instrument of brutal oppression of Shafilea and the other children.
"It really is a unique and extraordinary case."
She said that, within days, Ahmed had provided police with a "devastating statement" describing her sister's death.
"She then submitted to very close witness protection, which continued from that time until now and will continue indefinitely into the future," she said.
"It is an indefinite sentence and we say it is like a prison sentence but without the modest consolations of prison life.
"There is no doubting the risk of what she has done and there's no doubting the effect of her actions in transforming a particularly cruel and serious cold case into a successful prosecution.
"The purity of this young woman's motives are quite extraordinary and the pain of what she has gone through is also quite extraordinary."
PA
