Retaining the tricolour is a red-line issue for a united Ireland, Mary-Lou McDonald has claimed.
The Sinn Féin president believes there would be a "huge economic dividend and potential" in reunification and it would provide a chance to properly deal with healthcare across the island.
However, she ruled out altering the Irish flag to perhaps include a red hand to reflect the unionist tradition.
"The tricolour is our flag, I think it's inclusive it represents the green and the orange, Amhrán na bhFiann is our national anthem," she told Newstalk's Pat Kenny Show.
She described Brexit a "constitutional earthquake" which will change everything on both sides of the border.
Separately, Ms McDonald refused to condemn the attempted murder of Arlene Foster's father during the Troubles.
The current leader of the DUP was present when her father, John Kelly, was shot in 1979.
While Ms McDonald said it was "wrong" that Ms Foster had witnessed the attack, she said she would not be going down the "rabbit hole" of condemnation.
Ms McDonald said: "The politics of condemnation is a rabbit hole that I will not go down because it becomes a tit-for-tat, you-said-I-said, I think that serves nobody's interest
Asked how often she speaks with Ms Foster given the fact that the Assembly has not been up and running for almost three years, she said: "We have contact that is sometimes by telephone, more often it's face to face," said Ms McDonald.
Meanwhile Sinn Féin has revealed that Michelle O'Neill held on to her post as the party's vice president with two-thirds of the vote last Saturday.