Patsy Stevenson said recent reports of gatherings at Number 10 are “appalling” and that the Government is not “above the law”.
Images of Ms Stevenson being handcuffed and held down by two male officers sparked anger over Scotland Yard’s policing of the vigil on March 13 last year.
She was arrested and issued with a £200 fixed-penalty notice.
They should apologise, obviously, because they did something wrong, but that shouldn't mean that they are not held accountable for their actions
The 29-year-old physics student said she does not understand how the gatherings at Number 10 were “allowed to happen”, when she was thrown to the ground while mourning another woman’s murder.
She told the PA news agency: “It doesn’t make sense in my head. And it just really enforces the idea that the Government can get away with whatever they want.”
Ms Stevenson, from Egham, Surrey, is currently involved in legal action against the Metropolitan Police over its actions at the March 13 vigil.
She said the force must not wait for the findings of Sue Gray’s inquiry into the Downing Street gatherings before launching a full investigation.
The Met has said that if the inquiry identifies evidence of behaviour that is potentially a criminal offence, it will be passed to the force “for further consideration”.
Ms Stevenson said: “If they want to have any trust with the public, they need to investigate it immediately, and treat it the same as how they would treat it if it was a party with anyone else.”
If those involved breached regulations but are not held accountable, she believes members of the public who have been fined should have their money returned.
On Wednesday, Boris Johnson apologised for attending a “bring your own booze” party in the Downing Street garden in May 2020, saying he believed it was a work event.
Downing Street has since apologised to Buckingham Palace after it emerged parties were held in Number 10 the day before the Duke of Edinburgh’s funeral in April last year.
Ms Stevenson continued: “If I apologise for going to the vigil, would I get my money back? Would I be let off the hook? No.
“So why does an apology matter? They should apologise, obviously, because they did something wrong, but that shouldn’t mean that they are not held accountable for their actions. Saying sorry isn’t a consequence.”