Elizabeth MacKenzie, 47, and her daughter Angel, 13, bubbled with friend Petra, 36, and her daughter Kacie, 12.
The women are both stay-at-home carers for vulnerable family members and 'bubbled up' to offer each other respite and childcare support on weekends.
But after an apparent 'tip off' about a party at the home, police turned up and found the girls watching a film with hot chocolates.
They found a third child there - a little girl, 13, who was officially living with the MacKenzie family for a month while her single dad recovered from a broken back after a work accident.
Police accused the mum of facilitating a gathering of two or more people in a private dwelling.
It happened just two weeks before Downing Street's alleged Christmas gathering, which is said to have involved 50 workers break rules to party.
Carer Elizabeth from Preston, Lancashire, was hauled in front of magistrates on December 2.
The single mum now has to pay a fine of £834 for the breach of rules and will see £20 a month disappear from her bank account each month as a result.
The fine has tipped her overbudget and she has been forced to look for debt consolidation solutions.
Elizabeth, a full time carer to disabled daughter Kayleigh, 26, said: "It makes me angry. I get fined for looking after a child and made a fool out of by a police officer whilst Boris sips wine and parties - how is that fair?
"The court made me feel like I put lives at risk but I was just looking after children who were trapped inside anyway and not allowed out to play. My son loves politics and was very upset because of the Hancock thing and now Boris with his party two weeks after the night that I've been fined for babysitting - it's just so unfair.
"I'm a single parent with underlying health issues and the police scared me and the kids when they came to our house that night. I was in a bubble with the mum of the child who was staying at ours - we helped each other with looking after the kids regularly as we are both stay-at-home carers.
"I only moved here from Scotland four years ago, I have nobody else here. I have chronic back pain and nerve damage so I don't keep well myself. It was very important that I had that bubble for support and help.
"They kept saying it was a birthday party but it wasn't - we had one child staying with us for the night, there was no music, just homework followed by a film with snacks. I have never been in trouble before and I was made to feel like a criminal. I can't believe this has happened to us."
Elizabeth had her three children, Kayleigh, 26, Lewis, 19, and Angel, 13, living with her last December when the alleged rule break happened on December 5.
She also had a friend's daughter, 13, living her for three weeks after schools shut. The girl's dad was in an accident at work that left him unable to walk.
Elizabeth and Kacie's mum Petra are both stay-at-home carers and had formed a bubble, taking it in turns to babysit each other's daughters every weekend.
Petra's daughter Kacie, 13, was staying over for the night of what just so happened to be Angel's 13th birthday, as part of regular childcare arrangements.
Kacie, Angel and the third pal were watching White Chicks with hot chocolates in their pyjamas after finishing their homework when Elizabeth got a knock at the door from police at around 11pm.
Elizabeth said: "The police came to the door and explained they'd had a call saying that I was having a party. I only had the kids who lived with me at home plus one other child whose family I was in a bubble with.
"All the girls did was do their homework, practice some TikTok dances, watched 'White Chicks' with hot chocolates and then upstairs for face masks in their pyjamas - hardly a party.
"A male police officer said we couldn't have a bubble in Tier Three and then stuck his foot in the door, saying he was coming in to check whilst I was explaining the situation to his female colleague.
"That annoyed me so I said no way was he coming in like that but the other police officers could.
"The female police officer said if I sent Kacie home, then I would just get a warning, so I phoned Kacie's mum to explain what happened and my brother took her home - I had to get her dressed at 11:30pm out of her pyjamas.
"With Kacie gone, the male police officer then told me he didn't like my attitude, to which I said I didn't like his, and then he pulled out his iPad thing and said he's fining me."
Appearing at Lancashire Magistrates Court on December 2 this year, Elizabeth was found guilty of participating in the gathering of two or more people in a private dwelling in a Tier Three area.
The court ruled that Elizabeth had breached lockdown rules by having the other girl under her care while in a bubble with Kacie's family.
With the night in question was just 13 days before 50 government employees had an alleged party on December 18.
She said: "I'm a stay-at-home carer and my past jobs have been in childcare and working with kids with extra needs - I would never put their health at risk. I have really bad depression and the suggestion that I'd do anything to hurt the kids has really hit me.
"I couldn't even have my main witness - Kacie's mum Petra - at court with me because she was in hospital so I was completely alone. Angel was crying in court - she kept saying that if I hadn't got her a birthday cake, then it would have been ok.
"They don't realise how much it's affected mine or Angel's mental health. She's a quiet girl who never goes out anyway as she gets scared. It makes me angry. I help out because a man had a bad accident and I have a support bubble, but I get a huge fine and made a fool out of by a police officer whilst Boris sips wine and parties, how is that fair?
"I was made to feel like I put people's lives at risk which made me cry, so yes, I'm so angry at the system, I'm angry at Boris, I'm angry at the police and magistrates but mostly I'm hurt because of how low they made me feel."