Emma Jones’ 18-year-old daughter, Ruby Fuller, died on 15 May 2020 after a short battle with blood cancer.
The same day the Prime Minister, Boris Johnson, was pictured eating cheese and drinking wine in the gardens of Downing Street despite lockdown rules.
Mrs Jones told Sky News she feels a range of emotions on learning the news about the party.
“I feel upset, angry and also stupid that we followed the rules so closely. We felt it was so important to do so,” she said.
“It is just so incredibly insulting and I think it just makes a horrible situation just that much worse.
“What is particularly infuriating now is that evidence is really mounting and it feels like it’s time for the prime minister to put his hands up and accept and acknowledge that what they did was very wrong and very insulting to all those people, or families like ourselves, who made enormous sacrifices.”
Downing Street lockdown party: What were the COVID rules on May 2020?
Ruby had been treated for blood cancer for 10 months and was getting better.
Three weeks before she died, however, Ruby relapsed – and by that stage she was out of options.
Her mother said: “We were lucky in that she was at home so she was able to see me, her father and her sister.
“But we were the only people other than hospice care staff who came in to look after her who she could see during that time.
“She couldn’t say goodbye to her friends or grandparents, or cousins.
“They had to say goodbye on Zoom. That was very hard for Ruby but also for her friends and our family.
“And we did that because those were the rules. Now it appears those rules were for everybody except the government.
“We deserve better than this.”
If Ruby was alive now she would be “absolutely spitting mad”, Mrs Jones said.
“She asked to be remembered by the motto Live Kindly, Live Loudly.
“She believed that being kind was the most important thing but she also believed very strongly in calling out injustice.
“She would not be calm if she was alive right now, she would have made a protest banner and been banging on the gate at number 10.”
The family has set up a special fund in memory of Ruby, named “Live Kindly, Live Loudly“, to raise money for research into T-cell lymphoma and leukaemia, which has so far raised more than £122,000.
Mrs Jones spoke out as Downing Street remains engulfed in a storm of controversy over the so-called “partygate” scandal – piling pressure on the PM.
A senior Conservative told Sky News that claims Mr Johnson and wife Carrie attended a drinks event in the Downing Street garden during the first national lockdown were “indefensible” and “as bad as it gets”.
But the House of Commons heard on Tuesday how the prime minister is “going nowhere” and “retains the confidence of the people of this country”.
Answering an urgent question tabled by Labour Deputy Leader, Angela Rayner, Paymaster General Michael Ellis told MPs he has “confidence” in Mr Johnson’s “integrity and honour”.
Senior civil servant Sue Gray has been tasked with investigating multiple allegations of COVID rule-breaches in government.