The pop star-turned-fashion mogul was part of the girl group's initial get together last year (18), but made it clear she was not on board for any concerts.
Her four bandmates clearly hoped she would change her mind - but she didn't, and she was a no-show for the recent run of sell-out U.K. concerts.
"It took me a lot of courage not to go on tour with the Spice Girls again, but to be the one who says, 'You know, I’m not doing it because things feel different now than they used to,' " she tells Vogue Germany. "I'd rather concentrate on my family and my company."
"I'm 45 now and very happy to be the woman I am... I'm not trying to change, I want to be the best version of myself. Before I turned 40, I wasn't that confident. I learned to listen to my gut feeling."
The comment comes a week after former bandmate Melanie C a.k.a. Melanie Chisholm revealed the girls had such a good time performing together again, they now hope to extend their reunion and tour the world.
"We don't want it to end," she said. "We've had an incredible run here in the U.K. We'd really like to get further afield."