But Mr Key said Ms Collins had "over-reached".
"My view, she has probably learnt a lesson from the experience and I don't think we'll see it again."
He had "long and meaningful" discussions with Ms Collins yesterday, but did not ask her to stand down.
"What I did do is make it quite clear that I think in the end we need to deal with this situation better. I think she's a very good minister and she can do that."
Ms Collins needed to "take a moment" to reflect on her Oravida dinner and her actions yesterday.
Katie Bradford. Photo / NZ Herald
"At the end of the day ministers should avoid at least the perceptions of conflicts of interest. She unfortunately didn't ... and she has had to wear the brunt of that.
"But in the end you do need to soak up that pressure as a minister. I think she will and I think you won't see what you've seen in the past."
Being in politics was a tough business, but politicians knew that when they signed up to being a minister, he said.
A spokeswoman for Ms Collins said she had acknowledged she shouldn't have brought Katie Bradford into the discussion.
"She's apologised publicly and is hoping to talk to Katie shortly. Going forward, anything else she has to say on the matter will be with Katie herself which is the most appropriate thing to do."
According to Bradford's TVNZ boss, John Gillespie, Ms Collins admitted to him that Bradford had never asked her for help.
Before apologising on Twitter to Bradford, Ms Collins hinted in an interview with TV3's Brook Sabin that she could dish up more dirt on the press gallery.
"You might just find I get recall on all sorts of things. We'll just wait and see. I think it is very important when the media want to raise issues about behaviours, they need to understand that they sometimes can be very inappropriate as well."
Ms Collins' parting shot after the interview suggests she blames the media for Mr Williamson's fate, rather than Mr Williamson himself or the Prime Minister, who asked for his resignation.
"Let's see if you hold your own people to account after you've done what you've done to Maurice," she said to the TV3 reporter.
When Ms Collins was asked yesterday to comment on a Herald on Sunday story about Labour MP Ross Robertson approaching her about his police officer daughter's leave, she told TV3: "It's just like when a member of the press gallery approached me about how her then husband was having difficulty in becoming recruited by New Zealand Police.
She said this was a problem and she had been told that her husband wasn't going to be acceptable as a police recruit because of her family connections."
Bradford's mother is the veteran protester and former Green MP Sue Bradford.
Ms Collins tweeted last night: "Katie, I was answering questions about wider public engagement. Yr example came to mind. Reflected on that. Shouldnt have. Sorry."
Katie Bradford said she'd had a good working relationship with Ms Collins but had never asked for a personal favour and was completely surprised by the comments.
"Back in 2010 my ex-partner was considering applying for the police force - at the time it had been suggested to him that he might have an issue with being accepted.
"I recall that this came up in an informal conversation between the minister and me but I never asked her to intervene."
Her partner never formally applied to join the police.
On Friday night Bradford told the television audience she hadn't seen Ms Collins at the National's northern conference in Auckland. Ms Collins had been there and took to Twitter on Saturday night accusing Bradford of being biased and demanding an apology.
