The Spice Girls star, who will also play the part of Mary Magdalene in the Jesus Christ Superstar arena tour, admitted that she struggled to reject unsuitable contestants.
Copyright: ITV"There have been dramas, I'm not gonna lie, but we've always tried to be constructive," she said.
"In this industry you have to accept that while you might be talented you might not be quite right for a role. It's hard for anybody to take rejection, so I was quite sensitive."
Praising fellow mentor Jason Donovan, Mel C said: "Jason Donovan was amazing. He's such a lovely man and so professional - it was like learning from the master. We had so much fun."
The 38-year-old singer acknowledged the religious controversy surrounding the rock opera, adding: "Of course, and all the way down the line we're reminded again and again from Andrew and Tim Rice that it was never meant to be any comment on religion.
"It's really an artistic piece that's inspired by events that may or may not have happened. But you have to respect that people have very strong views and opinions about this. So I think we always have that in mind and acknowledge that."
Superstar kicks off this Saturday (July 7) at 7.25pm on ITV1.
Watch the trailer for Superstar below: