"I think the thing with the PM is he is very relaxed and sure in himself, in his own leadership," she said.
"That's why he doesn't feel threatened by other ministers doing a good job. That is different from weak leaders. "
Until this past fortnight, Judith Collins has been cementing her place as National's Boadicea, gaining profile with adept handling of justice and ACC this term and her famously combative style and put-downs.
However, her helmet has slipped badly. As Mr Key put it , she misled the media by omission about the level of contact she had in China with principals of the Oravida company, of which her husband is a director. The furore has derailed the party's carefully planned strides towards the September 20 election.
She has resisted tears in the House but has been in tears this week: "One of the reasons I try desperately hard to keep my family out of the limelight, even though I have been stunningly unsuccessful in the last few weeks, is that I get really hurt when they get hurt and they can't fight back."
The former lawyer entered Parliament the same year as Mr Key, 2002.
She raised hackles soon afterwards with her blunt assessment of how hopeless the party's central campaign had been - under the leadership of Bill English and president Michelle Boag who deposed John Slater.
Mr Slater's son and influential Whaleoil blogger Cameron Slater is a good friend and supporter of Ms Collins.
She is said to have a strong network of loyal supporters including Maurice Williamson, Jami-Lee Ross and Peseta Sam Lotu Iga.
She has never shown a hint of disloyalty to Mr Key but it is a given that she would go for the leadership if National loses this year's election.
The contenders would probably be Ms Collins and Economic Development Minister Steven Joyce. If the leadership succession were later, the contenders would more likely be the generation that includes Simon Bridges and Amy Adams.
Some in the caucus believe Collins has damaged her leadership prospects. More believe it won't have any long-term effect. Acolytes believes the silver lining is that she has shown a more human side.
Asked if she thought it was time to show a little more humility, she said: "Yes, I probably do. Many people who know me well or who I work with know I spend a lot of time out with the front line staff.
"But I have to say that probably as an MP I am far more combative with other MPs than I ever am with the people I work with," she said.
"That is my style and I really should try not to be so much so."