The Absolutely Fabulous star has penned Spice Girls musical Viva Forever!, which had its world premiere at the Piccadilly Theatre in London's West End tonight (December 11).
Saunders told The Mirror that she knew she "really, really had to write" the musical after joining forces with Mel B, Mel C, Emma Bunton, Victoria Beckham and Geri Halliwell in 1997 for Comic Relief.
The 54-year-old said that they have stayed friends ever since, adding: "They were so great with my kids and the best thing about them is you could go to see one of their shows and take a child or your grandmother and everybody would enjoy it. They were never over-sexualised."
She went on to say: "The thought of a Spice Girls musical written by somebody else was not acceptable. Because I was so close to them, I couldn't let it slip through my fingers.
"People don't actually realise how incredible the Spice Girls pop songs were. They are genius."
Photo gallery - Spice Girls musical Viva Forever! premiere:
"Viva was a great project to do because it took a long time. Being busy during that time was a welcome distraction."
Saunders said that she is confident the show will receive a positive response.
"The general feeling for the Spice Girls is so good I don't think anybody would not enjoy it," she stated. "It's a pretty good show, even if I do say so myself.
"I want this to hit the target audience. I want it to have a broad spectrum of viewers. A friend of mine brought her 73-year-old mother the other night who has never really heard a Spice Girls song and she cried all the way through. So that's a good sign."
She added: "It sounds dangerous saying the musical is relevant for our time, doesn't it? You worry that it could fall flat on its face. But it had to be about now and not be set in the past and be based on nostalgia."
Watch a launch video of the Spice Girls musical Viva Forever! below: