She was named acting first minister after the mass resignation of her party colleagues amid a crisis sparked by a murder linked to members of the IRA.
The senior Democratic Unionist said: “I have been placed there as a gatekeeper to make sure that Sinn Fein and the SDLP ministers don’t take actions that will damage Northern Ireland and principally, let’s be honest, that damage the unionist community.
“If anybody knows me and indeed knows the Democratic Unionist Party, they know that I’m not going to put at risk to the people of Northern Ireland the possibility that rogue Sinn Fein or renegade SDLP ministers are going to take decisions that will harm the community in Northern Ireland.”
DUP leader Peter Robinson stepped aside as First Minister over unionist concerns about paramilitarism - Sinn Fein contains many former IRA members - and has asked Mrs Foster, his finance minister, to remain in the Executive to prevent nationalists from taking over key ministerial posts.
But her remarks drew criticism from Sinn Fein’s Gerry Kelly, who described them as “bigoted” and a “throwback” to the past.
He said: “To make this attack on nationalism - because it wasn’t just republicanism, but on nationalism - and call ministers ‘rogue ministers’ is a complete nonsense.”
The unionist walkout from the mandatory coalition came after the DUP failed to get the Assembly adjourned for a period to allow crisis talks to address the implications of the murder of Kevin McGuigan.
The political furore over the killing intensified on Wednesday when three senior republicans were arrested in connection with the murder.
The trio and a woman have been released unconditionally, police said.
As he announced the resignations, Mr Robinson repeated a demand for the Government to suspend the institutions outright to enable space for the talks to happen.
Northern Ireland Secretary Theresa Villiers last night rejected the call.
The fallout from the murder of Mr McGuigan has already seen the Ulster Unionists resign their one ministerial post. The exit of Mr Robinson along with three of the DUP’s four other ministers, and its one junior minister, has left the 13 minister administration in freefall.
The departments of health and social care; social development; enterprise, trade and investment; and regional development are now effectively rudderless.
Collapse of power-sharing is not inevitable but the crisis follows a day of dramatic developments at Stormont on Thursday.