A spokeswoman said neither the Prime Minister nor his wife Samantha wrote letters in support of the application and that "the normal application process was followed throughout".
"As is usual, Mrs Cameron was named on her application as her employer," Number 10 said of the successful bid that was granted in late 2010.
Questions were raised about Mr Cameron's use of foreign domestic help after Home Office minister James Brokenshire said the wealthy had been the main winners from Britain's openness to labour from abroad, because they had to pay less for tradesmen and services.
The losers had been ordinary workers whose wages had stagnated, he added.
Mr Cameron recruited Gita Lima through Kalayaan, a charity that helps immigrants to escape abusive bosses.
"The point is that the Prime Minister's nanny is someone who has come here, works hard and is now a British citizen," a spokeswoman for Downing Street said.
"You can expect that the Prime Minister would follow the normal process."
Deputy Prime Minister Nick Clegg disclosed he employs a Belgian national as a domestic help.