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 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 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, after previously pleading guilty to robbery.
She helped organise the crime at her parents' home in Warrington in August 2010.
Sentencing Alesha, 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 life will be overshadowed by all that has happened, and it may be a long time before you achieve peace of mind and any normality."
He said robbery in the home was a serious crime and the normal sentence for this offence would be a significant jail term, even for someone of good character who pled guilty.
Handing her the suspended term, the judge said she would be supervised by the probation service and have to undergo continuing mental health treatment, adding: "I am confident you will not re-offend."