Her memoir, A Light That Never Goes Out, was published posthumously on Friday.
Ms Shanley died at the age of 51 last February after being diagnosed with stage 4 breast cancer.
Her husband, Conor Ferguson, appeared on The Late Late Show last night to talk about his wife and her new book.
On the show, Mr Ferguson talked about the “American option” where she was eligible to be a candidate in a medical programme.
He said that one woman, with the same diagnoses as Ms Shanley, had been cured.
Mr Ferguson explained that she was accepted onto the programme in the US and that it was a “last beacon of hope”.
He explained the process, saying: “They take tissue from the body, and then they propagate cells and then they use those cells back in the body to fight the cancer.
“But it takes months and months to propagate the cells. And within that time, unfortunately, Keelin’s condition deteriorated too quickly, too much.
“We just got to a point where an email came in one day to her from the hospital saying: ‘unfortunately, you are not eligible any more as a candidate.’
“So that was tough because that was sort of Keelin’s last beacon of hope.
“So that was hard for her. It was hard for all of us and telling the kids was really hard.”
Mr Ferguson said that Ms Shanley had always drip-fed their kids information and that when it came to telling them there was no more treatment “it was really really hard”.
“But they were just so brave.” They were 11 and 13 at that time.
Speaking about the new book, Mr Ferguson said that Keelin wanted to leave a story behind for her kids.
“She just wants them to know her and what she’d done and how she lived her life and how she looked at things.
“Not necessarily as a guide book for how to live but just to leave a bit of herself behind.
“But also, the book really kind of functioned to help her remember who she was as a person herself.
“Cancer can defeat the person and make you feel like you’re just a number. You’re a patient and you’re working toward’s someone else’s timetable.
“And that isn’t the case. You’re still the same person. The book allowed her to reconnect with herself and to go back and see the work that she’d done.
Mr Ferguson added that being reflective wasn’t a natural process for Keelin but that it was good for her.
On the show, the Hothouse Flowers performed Lou Reed’s Perfect Day, which was played at the couple’s wedding and at Keelin’s funeral in tribute to her.