Ms McDonald said Sinn Féin has always been an enthusiastic participant in power sharing, however, she said the party has run into immovable and ongoing roadblocks.
"So It's time to call Mr Johnson's fantasy for what it is - profoundly stupid and immeasurably unsafe".
The "Northern Ireland-only" backstop is not new.More news: British lawmakers reject holding snap elections ahead of Brexit
She said that as the October 31 Brexit deadline approaches and "pressure mounts" neither Taoiseach Leo Varakdkar nor European Union negotiator Michel Barnier "can blink in the face of Tory intransigence because so much is at stake".
Speculation on the possibility of a backstop specifically designed and exclusive to Northern Ireland has significantly increased in the last 48 hours.
Following a meeting between Boris Johnson and Taoiseach Leo Varadkar in Dublin, Mrs Foster said she was "encouraged" by the British Prime Minister's commitment to getting "a sensible deal".
Ms McDonald said the money was bequeathed to Sinn Fein "within all of the rules and regulations and will be spent within the rules and regulations".More news: Yelich out for season with fractured knee cap
Ms McDonald was asked if the DUP or the Northern Ireland Assembly should have a final say on what is agreed.
She added that she believed a solution had been reached 12 months ago but "the DUP refused to play ball" and since then the DUP has been distracted by Brexit.
Sinn Féin lost half of its councillors and two of its MEPs in the elections in May.
Ms McDonald said it would be "inappropriate to comment" on whether Mr Hampton had mental health issues.More news: Will cost just $4.99, launches on November 1st
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