Mel C was inspired to opt out of the Spice Girls reunion by former bandmate Victoria Beckham's decision not to rejoin, the singer said.
The musician also explained how her choice to put herself first and not be "walked over" was down to wanting to be a good role model for her daughter.
The remaining three members of the girl band - Emma Bunton, Melanie Brown and Geri Horner - are set to reunite next year to celebrate the 20th anniversary of the Spice Girls' debut album.
Mel C told Grazia magazine: "I had concerns about Victoria not being involved and started having second thoughts.
"When I'm a solo artist, my life is my own, but when you become part of the group again, it's much higher profile.
"You become part of something you can't control. In the past, I haven't always enjoyed that level of pressure and exposure. One day I just woke up and realised I couldn't do it."
Of her seven-year-old daughter Scarlett, she said: "Being a mum to a little girl means I have to set a good example and I treat myself better than I used to.
"I want her to be a strong woman, so I can't allow myself to be walked over. I have to lead by example.
"Instead of rejoining the band, I've made a solo record that I'm incredibly proud of and that's taught me that taking risks can pay off."
However, Mel C looks back on her days as a member of the Spice Girls fondly and said the thing she is most proud of from her time in the band was helping people in different areas of their lives.
She said: "These days, people who were fans at a very young age approach me all the time and tell me we inspired them in their careers or gave them the confidence to come out as gay.
"We were such a big part of so many people's childhoods and that's the thing I'm most proud of."
Grazia magazine is on sale now.