The Sinn Féin leader has said she will speak to Sinn Féin MLA Conor Murphy about meeting the family of Paul Quinn, following remarks he made about the young man.
The 21-year-old, from Annamar, Cullyhanna, Co Armagh, was murdered in Co Monaghan in 2007.
Mary Lou McDonald said she wanted the matter clarified and would be willing to meet Paul's mother, Breege, herself.
Asked if she was concerned that issues from the past would derail Sinn Féin in the closing days of the campaign, Ms McDonald said past issues being raised to cause damage or score political points "is not where people are at".
She said: "I don't think people want an unseemly row where pain is traded and fingers are pointed."
She also said she is not surprised by Sinn Féin's performance in recent opinion polls, because of "the extent of the appetite for change" her party is meeting on the campaign trail
Ms McDonald repeated that she would not enter into a confidence and supply deal with Fianna Fáil or Fine Gael, describing it as a "con job" which was "fundamentally dishonest".
She added that she will be doing her homework for tonight's RTÉ leaders' debate and was looking forward to taking part.
She said she is interested to see how the other two leaders - Leo Varadkar and Micheál Martin - will "expose" her as they have promised.
She said she hopes it will help people crystallize their decision and encourage them to come out and vote.
Ms McDonald was speaking in Ringsend at the launch of a billboard about Sinn Féin's campaign to tackle rising insurance premiums.