The Sinn Féin leader said she believes this will be a "hugely important election" in which the dominance of Fine Gael and Fianna Fáil can be "smashed."
Mary Lou McDonald said the leaders of both parties have an "obsession" with criticising Sinn Féin and talking about themselves and she said the government needs an "adult in the room" to keep the focus on the people.
She said what she described as "project fear" was well underway and that she would respond to that by "calmly" setting out her party's manifesto and giving people hope.
Speaking before RTÉ's decision to allow Ms McDonald take part in tomorrow's leaders' debate, she said the original decision to allow just Leo Varadkar and Mícheal Martin to take part was "farcical"
The Sinn Féin leader also said she does not believe her party's proposal to freeze rents is unconstitutional because it is time limited.
Mary Lou McDonald said Fianna Fáil has "flip-flopped" on the issue and that her party have been pursuing the issue for a number of years but that Fianna Fáil and Fine Gael have opposed that.