An "out of control" woman waved a knife at a car window a three-year-old child was sitting behind screaming in fear.
Chelsea Russell said she "lost her head" when dad-of-three David Law intervened in an argument she was having with her girlfriend.
Liverpool Crown Court heard Mr Law and his wife Amy stopped their car when they saw Shauna Aston distressed in the street.
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But when Mr Law prevented Russell from grabbing her partner, the 23-year-old went home and got a five to six inch knife.
Russell slashed the blade towards the victim in front of his terrified children - aged three, seven and eight - then attacked their car.
The court heard the family were travelling in a Ford Kuga along Stonebridge Lane, in Croxteth, on September 25 last year.
Frank Dillon, prosecuting, said front seat passenger Mr Law "became aware of a young woman who turned out to be the defendant's partner, who was clearly upset".
Mrs Law stopped the car and her husband spoke with crying Miss Aston, out of concern for her safety.
He saw Russell, of Stonedale Crescent, Croxteth, cycling away on a bike, but she returned and started "shouting and screaming" at him.
Mr Dillon said: "The defendant tried to grab at her partner but Mr Law sought to protect her, simply by putting his arm in the way.
"This caused the defendant to scream again. She cycled off again and said she was going to get her dad."
Mr Law decided to call the police and waited for officers to arrive, but Russell appeared again, with the blade.
Mr Dillon said she dropped her bike and quickly walked towards him with the knife in her clenched right fist.
He said: "She was shouting and screaming. She brandished the knife in a slashing motion at about chest height."
The court heard she did this around six times, but each time Mr Law stepped backwards, out of reach.
Mr Dillon said: "The children in the car were screaming at what they witnessed."
As their dad got back in the car and told Russell to move away, she shouted "get in your f***ing car" and started attacking the vehicle.
Mr Dillon said: "The children were still screaming hysterically. She kicked at the passenger door and kicked it closed, because it had been slightly open.
"She stopped at the rear passenger window where the three-year-old passenger was sitting and waved the knife towards that window - it actually touched the car window.
"At this point a police van turned up and a police officer ran towards the defendant."
Russell caused £500 of damage to the Kuga, including a scratch to the rear passenger side window.
She was arrested and gave a no comment interview.
Russell was charged with possessing a bladed article in public, attempted wounding with intent to cause grievous bodily harm against Mr Law, criminal damage and common assault against Miss Aston, all of which she denied.
Prosecutors offered no evidence on the attempted wounding with intent and common assault charges after she admitted a charge of affray, possessing a bladed article in public and criminal damage.
Russell has 18 previous convictions for 28 offences, including multiple offences of criminal damage and battery, and multiple breaches of community orders and a Criminal Behaviour Order.
William Beardmore, defending, accepted she had a "very unattractive" criminal record but asked for "one final chance".
He said: "In 2018 she was diagnosed with Asperger's syndrome. That's had an impact on her life and perhaps belatedly has offered some explanation to the way she has approached various different aspects of incidents in her past."
Mr Beardmore said Russell's behaviour was also affected by "misusing" cannabis since 2014, but she had now given it up.
He said her dad and Miss Aston were sitting in the public gallery offering support.
The lawyer accepted Russell had failed to take advantage of assistance given to her by the courts "time after time", but said she had found her first period in prison a "salutary experience".
He said: "She has missed her mother and father greatly. She has, over the period of almost four months that she has now spent in custody, become increasingly withdrawn and upset. She missed Christmas."
Mr Beardmore added: "She has heard the clang of the prison gate and it's had a very significant impact on her."
He said: "She told the author of the pre-sentence report that she lost her head, that this was a moment of madness."
Mr Beardmore said the couple were arguing and Mr Law "quite properly" became involved out of concern for Miss Aston.
He said Russell didn't know why she got a knife or waved it at Mr Law, but regretted it, was sorry, and understood how "terrifying" it must have been for the family.
Recorder Andrew McLoughlin, said Mr Law only acted out of concern for Miss Aston, but Russell chose to return "not with your father, but with a knife".
He said Mr Law avoided serious injury by moving backwards, before she damaged the car and waved the knife "in the direction of the children in the vehicle".
The judge told Russell: "You were just behaving in an out of control fashion."
He said he bore in mind her difficulties, but her inability to comply with court orders was "very unattractive".
Recorder McLoughlin jailed Russell for 12 months.
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