Arlene Foster has said the ill-fated Renewable Heat Incentive (RHI) scheme was not a "personal priority" for her and she wishes she had asked more questions about it.
Northern Ireland's former enterprise minister told the public inquiry into Stormont's botched green energy scheme that she had a "false sense of security" due to the scheme "working" in Great Britain.
The Democratic Unionist Party (DUP) leader also said she was "surprised" that her special adviser, Dr Andrew Crawford, had shared government documents about the scheme with his farmer cousin, and defended the part-time role he currently has with the party.
Mrs Foster was in charge of the planning of the scheme in 2012 before a series of fatal design flaws in the green subsidy project exposed Stormont to a huge overspend, paying out more than it cost to buy wood fuel.
She told the inquiry: "It's very difficult for me to go rooting about in a department to find out what isn't being brought up to me."
Asked whether she felt she should have done more "rooting around", Mrs Foster said: "Through hindsight, of course one wishes that I had asked more questions in relation to the Renewable Heat Incentive scheme.
Mrs Foster said the RHI scheme was not one she was "passionately looking at every day of the week".
Inquiry chairman Sir Patrick Coghlin asked Mrs Foster if she did not get the impression it was "a unique scheme" which was "highly unpredictable" and "highly volatile", adding: "That didn't help to boost it up a bit in your concerns?"
Mrs Foster said she was probably in a "false sense of security" that Great Britain was rolling the scheme out.
"I had the sense that it was working in GB, therefore it was coming to Northern Ireland," she said.
Mrs Foster said she was not aware that her adviser, Dr Crawford, had sent documents relating to the scheme to his cousin.
"But it's quite clearly something that he should not have been engaged in at that time, or indeed at any time," she said, adding that she was "surprised" at his actions.
Mrs Foster was asked about Dr Crawford still working for the DUP and it was suggested to her that this may lead people to believe that the party do not think what he did was "particularly serious".
She replied: "He is conducting some research in terms of Brexit for a member of the European Parliament. It's very much a backroom role. He's using his expertise in relation to that.
"It's not a full-time job by any means. I think that, given everything that happened in late 2016, early 2017, and I hear very clearly what you're asking me around the emails, and that was inappropriate and was disappointing from my point of view.
"But I don't think that that should bar a person from having part-time research employment forever and a day.
Sir Patrick replied that it was "hardly surprising" the media took an interest in him "given what happened".
Mrs Foster answered: "Well, I think the scale, Chair, of what happened to him, was difficult to take in at the time."
She said the media scrutiny was to be expected, but said what was not expected was "some of the more outrageous commentary around it".