"I don't want to go into detail but it was fairly inappropriate behaviour. I'm going to leave it up to the Prime Minister to deal with," Collins told RNZ.
Collins said the allegation was serious enough that if it were about a National MP, she would seek more information.
"This person is not my MP, and I thought she [Ardern] dealt with the matter relating to our MP well, and I'm not going to do anything other than treat this matter as something for her to deal with."
Asked about Collins' comments, Cabinet Minister Chris Hipkins told RNZ that it was a matter for the Prime Minister to comment on.
But he added that it seemed to be a contradiction for Collins to say she didn't want to get involved and then to put the matter into the public domain.
Collins said she hadn't thrown it into the public domain, but had been asked a direct question by MediaWorks and she had answered it.
MediaWorks had asked if she had "received anything about Labour ministers or Labour MPs", and Collins replied: "I have actually."
She said she wouldn't be "indulging in any attacks on Labour on these things".
"I spoke to the Prime Minister yesterday as we were coming out of Question Time. I said I had received such a tip-off and I did not want to receive any information on it.
"I would be asking the person to send it directly to her. She has provided me with an email address for that and that has been passed on to the person who contacted me."
A spokesperson for Ardern said there was no comment to make at this stage.
Collins yesterday condemned Falloon, calling him "a liar" and saying it had become apparent his actions were a "pattern of behaviour" with three more women coming forward yesterday to say they'd also received explicit images.
Falloon's political career began to unravel on June 30 when he sent a pornographic image - not of himself - to a university student. Police investigated but decided the matter didn't meet the threshold for prosecution.
The teen's parents then emailed the Prime Minister's office on Wednesday, which sought permission to pass the matter onto Collins.
The Herald understands Collins' chief of staff was emailed about the incident on Friday afternoon and Collins was told herself at 11.30am on Saturday.
The leader called him that day to discuss the allegations and summoned him to a meeting first thing on Monday morning to put it to him in person.
Collins said she asked Falloon on Monday whether there was anything else they should know about.
"We were told 'no'. That's an enormous lie and one that goes to the heart of whether or not I could trust him as an MP and so he's gone."
This morning Collins defended the initial framing of Falloon's behaviour as a mental health issue, saying she had been "very concerned" for Falloon's safety.
"One of my big concerns is that we would have a suicide," she told RNZ.
She arranged for Barbara Kuriger, the party's chief whip, to put Falloon on a plane to Christchurch, where he was collected by National's mental health spokesman Matt Doocey, who then drove Falloon to his parents' house in Ashburton.
Collins said what Falloon had done was "despicable", but he was "still a human being".
