The woman allegedly called an Asian chip shop worker, 28, a "terrorist" before throwing a charity box at him – just months after she was convicted of racially abusing his brother.
She is also alleged to have called the Huddersfield worker a "P**i" before he called police – but no further action was taken against her.
The second alleged offence came just three months before a video of her son allegedly bullying Syrian refugee Jamal, 15, went viral.
The 16-year-old faces assault charges after the clash at Almondbury Community School in Huddersfield, West Yorks.
It can now be revealed that his mum allegedly went in to a chip shop in Huddersfield to confront the owner on July 21 after she had been convicted of racially abusing him in March last year.
The woman, who cannot be named for legal reasons, was fined £162 at Kirklees Magistrates Court after admitting racially aggravated threatening behaviour in the earlier incident.
In March, the woman unleashed a volley of vile racist abuse before spitting at the owner. But staff now claim she went back after believing he had received a payout over the racist incident.
The owner wasn't working at the time of her second visit on July 21, but his brother is said to have been on the receiving end of her foul-mouthed rant.
Speaking about her return visit, the owner claimed: "She was ranting and raging accusing me of profiting from the first incident which wasn't true.
"My brother told her I hadn't and wasn't there but she just lost it. She called him a 'P**i' and 'terrorist."
He continued: "She then picked up a charity box from the counter and threw it at him.
"Thankfully she missed and he called the police. She was one angry woman."
The mum, whose 16-year-old son received death threats after the 'waterboarding' video went viral, was spoken to by police.
When contacted by The Sun Online, a spokesperson for West Yorkshire Police said: "A woman was questioned by police in relation to an incident in Westgate, Huddersfield on July 21 2018.
"There was insufficient evidence to prosecute and no further action was taken."
The Sun Online was unable to reach the woman for comment on the claims.
In November, police confirmed that her son is set to be charged with assault over the 'waterboarding' incident.
A spokesman said: "A 16-year-old youth has been interviewed and reported for summons, for an offence of assault. He will appear at Youth Court in due course."
The clip which caused so much outrage shows Jamal with his arm in a cast being dragged to the floor by his neck as his tormentor says: "I'll drown you".
The alleged bully has now gone into hiding and told Tommy Robinson that he was "scared for his life" after the video showed Jamal being thrown to the ground and threatened on the school field.
He told the former English Defence League founder: "We went into hiding because we've had all these threats, rape threats, death threats."
The teenager denied to the Sun Online that he was bullying his classmate whose family fled the Syrian warzone to come to the UK and claimed the pair had been on "good terms".
However The Sun revealed that his brother was jailed after a Britain First rally erupted in violence.
Cops also said they were investigating footage of another attack on Jamal's sister, where a young girl in a headscarf was taunted and shoved by school pupils.
Jamal had suffered a broken wrist after an earlier incident at the school.
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