Fardosa Abdullahi gave plot ringleader Omar her mother's long black robe to help him flee London the day after the attacks in 2005.
Abdullahi, now 20, got engaged to Omar in an Islamic ceremony four days before he tried to blow up himself and fellow passengers at Warren Street Tube station.
She admitted helping him escape at an Old Bailey hearing last month but today her lawyer pleaded for her to be spared jail because she was now pregnant and had a history of mental illness.
It was claimed that Somalian-born Abdullahi, 17 at the time, came under pressure from the "domineering" Omar to help him.
But Judge Paul Worsley told her: "The message must go out that this court will not go soft on those who assist terrorists - even those who are young, vulnerable and under pressure, as you undoubtedly were."
He added: "Your responsibility to this country should have been greater than your responsibility to your husband or fiance, if such he was."
Her sentencing today brings to an end a series of cases in which 16 people have either been convicted of or admitted charges linked to the July 21 attacks.
The failed blasts, just two weeks after what the judge called the "carnage" of July 7 2005, when 52 innocent people and four terrorists were killed, sparked a massive manhunt.
Abdullahi lied to police about Omar's movements at a time when, the judge said, it was "imperative" they should not be misled.
She pretended she had not seen him since July 21 but in fact had accompanied him to Golders Green coach station on July 22 when he took a bus to Birmingham, where he was arrested five days later.
CCTV footage seen at his trial showed the 6ft 2ins terrorist dressed head to toe in a burka.
To make him look more like a woman he had also shaved his arms and was carrying a ladies' clutch handbag.
Omar was jailed for life with a minimum term of 40 years at Woolwich Crown Court last July along with three other bombers convicted of conspiracy to murder.
Abdullahi, of Grosvenor Court, Finchley, north London, pleaded guilty on June 5 at the Old Bailey to a charge of assisting an offender, but her plea could not be reported until restrictions were lifted today.
She admitted helping Omar create a disguise by "dressing as a Muslim woman", as well as providing him with a telephone and giving false information to police.
The judge said Abdullahi, who is 24 weeks pregnant, had "as strong a mitigation as is likely in a case such as this".
He said her personal circumstances and guilty plea meant he could reduce the prison sentence from five years.
"But prison it must be, to reflect the fact that anyone who assists those who set out to kill and maim on a scale not to be contemplated must receive punishment," the judge added.
Abdullahi showed no emotion as she was sentenced.
Emma Gargitter, prosecuting, told the court that she became engaged to Yassin Omar in an Islamic ceremony on July 17 - although she was not present at the time.
But there was confusion over the precise status of the couple's relationship, with Abdullahi later describing Omar as her "husband" to psychiatrists.
Jonathan Cooper QC, defending, said she was pressured into her actions by the "domineering" Omar, a supposedly devout Muslim who was seven years older than her, and whom she barely knew when she became engaged to him.
He said that following a serious assault she suffered in Somalia at the age of six, she had tried to take her life on several occasions and spent a number of periods in secure hospital accommodation in her childhood.
Psychiatrists have diagnosed her as having a "strong pre-existing susceptibility to pressure, being highly suggestible", he added.
Omar was introduced to the family, who believed he was a "holy man", through her brother, who knew him from North Finchley mosque.
But the relationship was "unequal in the extreme", Mr Cooper told the court.
"Omar was physically strong. He was domineering. He had spoken to her and the family approvingly about what he considered the duty to beat a disobedient wife."
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