"I think Sadiq Khan is doing a good job and it's wrong to say anything else - he's doing a good job", she told a press conference on Monday.
His brother, Mark, said on Facebook that Ms Archibald was one of those struck by the van in the initial attack.
Police said six women and four men arrested after the attack were still being questioned.
Police said they now had 10 people in custody after releasing two of the 12 people arrested on Sunday.
"A number of people have been detained and are at present being spoken to", the Metropolitan Police said in a statement. "It's about which leader and which team people trust to keep Britain safe", May said. His sister Melissa McMullan said "he was an inspiration".
Trump is mischaracterizing Khan's remarks as suggesting that people should not be concerned about terrorism.
She said providing more firearms for London police wouldn't be a sensible solution to the increased tempo of attacks, saying the strategy of having special mobile units of heavily armed officers is effective.
Trump added that the media "is working hard to sell it!" The three assailants were shot dead by police.
Khan's statement on Sunday morning condemned the attack and gave a number of details about what had happened and what measures were being taken in response. At least 21 people injured remain in critical condition.
Mourners held signs with messages such as "hate will not divide us" and "stand up to racism", while others carried balloons shaped as hearts. Foreign Minister Julie Bishop said Andrew Morrison received stitches for a stab wound to his neck and was on his way home to Australia.
The latest attack comes against the backdrop of parliamentary elections later in the week.
Campaigning resumed yesterday after being suspended for a day.
Dick and Mayor Sadiq Khan visited London Bridge as commuters returned to work after some security cordons were removed.
Tales of heroism emerged, with one British Transport Police officer taking on the attackers armed only with his baton before being stabbed in the head, face and leg. "One of my friends would let Abz babysit his daughter", Mimbo said.
Harun Khan, the secretary general of the Muslim Council of Britain, agreed with May that things must change.
She was one of seven people killed on Saturday night in the van and knife attack by the three Islamist terrorists. Masood was shot dead by police.
Pressure will also mount after it became clear that Butt, who was born in Pakistan, was linked to well-known radical organisations. Abedi died at the scene.
Scotland Yard said one person is still believed to be missing, and that family liaison officers have been deployed to support the victims' loved ones.More news: Timeline: How events unfolded in London's latest attack