Her family started to worry when they had not heard from her -- but then saw her on their TV screens on Saturday as she the entered the Big Brother house in the UK.
Her mother Jacinta told the Herald she had started to worry when there was no word from her daughter, and that the news she was on Big Brother came as a shock.
She said: "I knew nothing at all. I only found out when the media started calling to the door looking for the story. I could not believe it. I could kill her. The phone has been ringing all night and all day!"
And Noirin was not the only Kelly daughter causing concern for her family on Thursday night -- older sister Julie gave birth to her second child that night in Holles Street hospital.
Noirin's nervous mum said she started to piece things together after learning of Noirin's latest adventure.
She said: "She went to London a few months ago, and said she was meeting a friend. Later, a woman called here, I think she was Australian, and I thought it might be the friend Noirin had gone to see.
"It must have been the Big Brother auditions she was going to, but she never let us know. As far as I was aware, Noirin was in America."
Jacinta described Noirin as a "lucky" girl who always finds success.
"She would be the girl who could walk out and find gold," beamed Jacinta.
"But, my God, how will we handle all of this?"
Asked if she was a fan of Big Brother, Jacinta said that she preferred to watch nature channels, like Discovery and National Geographic.
She said: "I have seen Big Brother, but always switched it to something more interesting.
"I will watch it now, but if Noirin does anything silly I will have to look away," she added.
Noirin was a good athlete growing up, and competed with the Ballybrack Athletics Club until her mid to late teens.
Big Brother is not her first foray into reality TV. She also featured on MTV's Real World show in Sydney.
On that show, she proved to be a viewers' favourite after stripping topless to join her new friends in a hot tub.
It was on this show that she met American Isaac Stout, with whom she had a relationship.
But the friendship is said to have ended when Isaac said he couldn't keep up with Noirin's full-on antics.
He claimed: "All she wants to do is drink, party and get down."
All eyes will be on Noirin, now single again, in the Big Brother house to see if she makes a move on any of her fellow contestants.
Last night, she and Rodrigo Lopes, a 23-year-old student from Brazil, became the first to earn their status to enter the main house when she agreed to let Lopes to shave off her eyebrows.
However, viewing figures for launch night were down for the second year in a row.
The average audience for the start of the 10th series of Big Brother was 5.1 million, the broadcaster said, a fall of 300,000 from last year.
Viewing figures for Thursday night's show peaked at 5.4 million, also down on last year, when a high of 6.1 million tuned in.
BB10 launch night attracted 23pc of the available audience, again down on last year, when the show earned 25pc audience share.