The 18-year-old, who wowed the judges with her reworking of Prince's 'Purple Rain', said she was "determined" to try out for another Cowell show after being axed at last year's X Factor Boot Camp.
"When I didn't get any further on The X Factor it made me more determined to come back," she told Digital Spy.
"I've always wanted for Simon to hear me, so when I heard that he was judging Britain's Got Talent I really wanted to come back and audition.
"He's the main man really, I really wanted him to hear me. He were so lovely and I couldn't have wished for better comments from him."
Redfern also admitted that covering such an iconic track for her audition had been a "risk".
"It's a really old song, it's a classic song. I didn't want to ruin it and I didn't want to change [it]," she said.
"It were a risk and it were really hard, but I hope I did it well. I hope I kind of made it my own."
On whether she would play it safe in future performances, Redfern explained: "I don't know if I'm going to do a difficult song but I'm definitely going to change something up."
Britain's Got Talent continues Saturday (April 14) at 8pm on ITV1.
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Watch Chelsea Redfern perform 'Purple Rain' on Britain's Got Talent below: