I think she lied.
What would she get out of it? Well, look at where she first "revealed" the visit, two years after it supposedly happened. It was 1999, at Paul Bonacci's civil trial. Paul (the con artist who claimed he had participated in Johnny's kidnapping) had sued a number of people and institutions for being part of the Franklin Credit Union (a conspiracy theory/hoax from the 80s satanic panic era). The suit had been dismissed for all except one - Lawrence King, former director of the Franklin Credit Union, and the only reason it wasn't dismissed is that he didn't challenge it. That's because he was already imprisoned and destitute after having been caught embezzling from the bank. So Paul and his lawyer, far-right Nebraska politician John DeCamp, used the trial to air their conspiracy theories unopposed.
And that's where Noreen comes in. She had met with Paul years before and believed him - though Noreen had pretty much believed everyone who came to her claiming to have knowledge about Johnny. She fully bought into the idea that Johnny had been taken into a Pizzagate/Qanon-style elite p*******e ring, and cooperated with DeCamp. If you read her testimony at the Bonacci civil trial, that's what she's doing - supporting the conspiracy theory. After having outlined the whole thing, DeCamp asks her if she has any evidence for it, and she says yes: "my son visited me and confirmed Bonacci's story exactly."
I've seen claims that she was forced into saying it by the judge, since she was under oath, but that's not true. Everyone was there voluntarily, and the one questioning her was her friend and ally DeCamp. And she always intended to say it - she and DeCamp even tease early in her testimony that she has a bombshell to reveal. Johnny's visit was meant to boost Bonacci's story, that was the point and that was what she had to gain - support for the conspiracy theory she had bought into.
The last parts of her testimony is full on conspiracy theory screed. Mind control. MKUlktra. Satanic p*******es in the military. Things you usually see on poorly designed websites with malware-warnings, or email forwards from less discerning relatives. Bonacci won the lawsuit and a million in damages from King - not because he convinced the judge, but because it was a default decision since King never challenged it. Of course, King never paid. He didn't have the money and never would again.
Of course, if she was tricked by someone, I'd say the list of suspects is exactly one person long.