Craig has spent the last 72 hours in a storm of controversy. He stood down on Friday after board members called for a leadership review.
Christine Rankin said she was aware of the financial dispute. She said she had delivered an ultimatum to her former leader several weeks ago after learning information that "shocked" her.
"I believed it was very sound and I had to ask about it."
She said she met Craig but was not willing to say what issues caused her such alarm.
"I decided after the meeting that he needed to tell the board everything, and if he didn't I would."
Rankin said the board was still owed an explanation by Craig.
She was uncertain about her future with the party but would remain on the board for next weekend's meeting on the leadership.
"Colin begged me to stand and the only reason I did it was for him. Now I am so cross at myself about that."
Craig refused to comment on the information that shocked Rankin, saying it was a matter for the board.
He said he was prepared to take legal action against board member John Stringer over comments made on TV3's The Nation yesterday.
Stringer said there had been widespread concern from party members about the "awkwardness" of the relationship between Craig and MacGregor. While he did not have any evidence of a relationship, he said allegations of harassment had been levelled against Craig.
"[His comments were] quite disappointing, factually incorrect and I will require a retraction from him," Craig said. He was prepared to go to court if need be.
Board chairman Brian Dobbs said Stringer's comments were his own opinion and not representative of the board.
Craig said he would "absolutely" stand for its leadership again should the board support him.
Craig's judgment was questioned earlier this month over a now infamous sauna interview on TV3's late night show Newsworthy, where a shirtless Craig shared a shower with journalist David Farrier.
"I'm not sure I regret it but I'm totally willing to take correction and if, on balance, it was the wrong thing to do I've got to learn from that," he said.
Craig stressed he was speaking in a personal capacity as statements regarding the Conservative Party should now come from the board.