Asked about her goal for her new roles, she said: "I want other ministers to say 'Gosh I wish I had Corrections. Gosh I wish I had police.' That's what I want them to say."
First on her agenda was a meeting with Corrections chief executive Ray Smith this afternoon.
She planned to call in private prison operator Serco next week to discuss "what's gone wrong" at Mt Eden Corrections Facility.
She had no regrets about awarding the contract to Serco when she was Corrections Minister in 2010, though she noted that she was not directly involved in selecting the company.
"I don't regret at all having baselines that the public service can work against and to have some sort of tension there," she said.
Ms Collins, who has a reputation as a law and order hardliner, takes over Corrections when its focus is increasingly on rehabilitation.
She had no plans to change this direction, pointing out that she had doubled drug and alcohol treatment in prisons during her last stint as minister.
During the investiture ceremony, Ms Collins was in a joking mood.
"I was going to do all virginal white but I thought, 'let's not push it'," she said when complimented on her blue blazer.
After telling Prime Minister John Key that she planned to do shopping over the Christmas break, she said: "I need your permission for that now don't I?" -- an apparent reference to Mr Key's order that she give up her TV appearances, car sponsorship deals and newspaper column.
At the same ceremony, Mr Lotu-Iiga was handed the Local Government portfolio and Michael Woodhouse was given the Revenue role.
They were sworn in by Administrator of the Government Dame Sian Elias, who is standing in for Governor-General Sir Jerry Mateparae while he recovers from heart surgery.
