An ex-girlfriend went on the rampage when she found another woman in the home she owned with her former fiance.
Emilie Barber and Steven Wareing junior agreed he would buy her out and she would leave their house after they split.
But 23-year-old Barber believed there was a "rule" in place that he wouldn't bring another woman back to the property.
When she unexpectedly arrived at the house and discovered the opposite, Barber armed herself with a cutlery knife.
She used it to unscrew the lock to an en suite bathroom when Abigail French was inside, to attack her ex-partner and scratch his car, then to threaten his "terrified" mum and dad when they arrived.
Liverpool Crown Court heard the couple were together for around three years, became engaged and bought the house together in Bearwood Road, Kirkby, before splitting up in May 2020.
Simon Leong, prosecuting, said: "Mr Wareing jnr describes how an agreement was reached in June for him to buy out Barber's interest in the property and for her to vacate it."
Mr Leong said on the evening of July 23, "Mr Wareing jnr brought a friend by the name of Abigail French to the address".
He said: "The defendant unexpectedly turned up at about 8.30pm and let herself into the property.
"Miss French wanted to avoid a confrontation and locked herself within an en suite bathroom as the defendant made her way upstairs.
"The defendant grabbed hold of the door handle of the en suite bathroom trying to open it shouting 'who's in the toilet?'"
He said Barber left but returned with a "cutlery knife" from the kitchen, "the round head of which she used like a screwdriver to unlock the en suite bathroom door".
Mr Leong said: "Once open, the defendant began shouting at Miss French before Mr Wareing jnr stepped in between them.
"The defendant slapped him once to the face before poking him three or four times in the stomach with the end of the cutlery knife."
Mr Wareing jnr wasn't injured but had a sore face and both he and Miss French got in his Ford Focus, parked on the driveway.
His ex-girlfriend opened the front passenger door where Miss French was sitting and screamed and shouted while waving the knife around.
Mr Wareing jnr drove off, but before he did Barber caused a three to four inch scratch to the rear body work of his car.
He had spoken to his parents and Steven Wareing snr and his wife Lesley Wareing arrived at the house in their car.
They realised their son had left and that Barber was there with her nan, before they were "aggressively confronted" by Barber as they got back in their car.
She waved the knife and pointed it "aggressively" at the dad, then went to the front passenger seat and did the same to the mum.
Mr Leong said Barber went back to the house on August 10 when it was empty to collect some of her items.
However, she also stole a £50 XBox controller, which she bought Mr Wareing jnr for Christmas in 2019.
Barber, of Ashmuir Hey, Kirkby, originally denied any wrongdoing, but ahead of a trial she admitted affray, common assault, criminal damage and theft.
In a victim statement, Mr Wareing jnr said his fear Barber would return left him struggling to eat and sleep, which affected his Type 1 diabetes.
He said he was constantly checking his Ring video doorbell, looking over his shoulder and wondering whether he could trust again, adding: "Emilie was the first major girlfriend I ever had."
Mr Wareing snr said: "When I was threatened with the knife I felt scared for myself and my wife because I didn't know what Emilie was going to do with it."
He said he was left feeling anxious and nervous and had nightmares about his wife being stabbed.
Mrs Wareing said: "I was terrified that either me or my husband were going to be stabbed or even killed."
The registered blind mum described how she was left shaking and vomiting, while the stress affected her IBS.
Paul Becker, defending, said Barber, who has no previous convictions, was only 22 when the relationship ended.
He said: "Matters clearly became very bitter. The defendant acted unlawfully, irrationally, in a manner inconsistent with her character.
"She is extremely contrite and extremely embarrassed at the shame she has brought upon herself and her family."
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Mr Becker said remorseful Barber had "a lot of good things going for her'' and was a qualified dance teacher who had worked for airlines including Ryanair and Tui.
He said: "She has spent the last year working in a private care home with patients suffering from conditions such as dementia doing good work, earning good money as well, helping out people at a difficult time.
"Hopefully she will mature and learn her lesson and never come back before the courts again."
Mr Becker said the property had not yet been sold and Barber had problems regarding mortgage payments.
He said Barber now lived at her nan's home, who died during the pandemic when she had provided care for her.
The lawyer added that Barber had a new partner and said: "I understand they're happy and there are no problems."
Judge Louise Brandon told Barber: "It's clear from all I have read and heard about this case there were - as far as you were concerned in any case - certain rules in place about the shared use of your home."
The judge said Barber was of the understanding these "rules" were in place so the couple could "respect each other".
She said: "You were of the view Mr Wareing had broken these rules by bringing another woman back to your home."
Judge Brandon said it was fortunate Barber didn't injure Mr Wareing jnr, before she also confronted his parents.
She said: "It's clear you caused them considerable fear, distress and upset."
The judge said during the incident Mr Wareing was forced to leave his home "to get away from you and protect his friend".
Judge Brandon said Barber accepted any further dealings with him would be via a solicitor and she worked as a carer making "a positive contribution to society".
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The judge said the Probation Service believed work could be done to reduce her risk.
She said: "That work will be vital to protect any future partner you may have and to protect the public in the future."
Judge Brandon handed Barber 16 weeks in prison, suspended for 18 months, with a 25-day Rehabilitation Activity Requirement, 120 hours of unpaid work and a five-year restraining order.