Julie Hambleton, whose sister Maxine was killed in the IRA attack in 1974, accused ministers of trying to bury "the dark past" of government collusion with terrorists.
She was responding to a controversial law proposed by the Government which would give amnesty for those accused of killing or maiming people during the Troubles.
Speaking on the 48th anniversary of the bombings, Ms Hambleton, of the Justice4the21 campaign, said she believed "most soldiers" were opposed to the legislation.
"The soldiers say that if there is a case to be brought against them, then they are happy to go to court to face the prosecution, because there is no honour in amnesty, and there is no honour in this," she told GB News.
"This Conservative Government is trying to railroad this obscene piece of legislation through into the law books that will pardon murderers like the cowards, who came to our city, killed with impunity, and then ran away."
A total of 21 people were killed in the attacks on two city centre pubs in November 1974. Six men were convicted but later freed after their convictions were deemed unsafe due to police wrongdoing.
The new legislation has been opposed by all parties in Northern Ireland, including the DUP and Sinn Féin, who say it will mean victims’ families will not get the justice they deserve.
Ms Hambleton said the bill was "trying to rewrite history". "Conservative governments are trying to bury their own dirty, dark past of their own collusion," she said, adding that "thousands of families" wanted the legislation scrapped.
The bill has been championed by Veterans' Minister Johnny Mercer, who has campaigned to protect soldiers who served during the Troubles.