The author was close friends with the late Love Island presenter, who died by suicide in February aged 40.
Talking on the That Gaby Roslin podcast, O’Porter explained how being a mother to her two children with her husband, the actor Chris O’Dowd, gave her a sense of purpose following her friend’s death.
“When Caroline died it felt like someone had kicked me in my head and I couldn't get up - but I had to get up because I have two small children,” she said.
O’Porter and O’Dowd have two children together, Art, five, and Valentine, three.
“The week after she died, I kept saying to Chris, 'Who's going to make me laugh like that?'” O’Porter continued.
"I laughed until I wet my knickers when I talked to Caroline. Where is that going to go?
“She was only 40, but Chris and I kept saying that no one could have sucked more life out of those years than Caroline.”
The bestselling author went on to reference Flack’s successful career as a TV presenter and broadcaster.
“She ticked so many boxes of what people are supposed to achieve, and she achieved them at level 10,” she said.
"I wish Caroline had just hung on to see that the world was going to move on from what she thought everyone cared about."