She notably broke down in tears during her appearance on I'm A Celebrity… last year as she revealed her low self-esteem, comparing herself to model Amy Willerton.
"Every day I look in the mirror and go, 'God, I'm not pretty. I've got a very big nose," she told the diary camera.
"That's what most of the negative comments on Twitter are about – my nose.
"People say, 'Oh god, you look like a dolphin', or 'I didn't realise they let whales into the Olympics, but at least you should be able to swim faster.'
"I'd have it straightened. But I couldn't float the idea of having a nose job before, because with swimming you only get two weeks off a year.
"Would I have it done now? I'd probably have it straightened. But it's really got to suit your face."
Rebecca went on to say that she found criticism about her appearance the most challenging aspect of competing at the Olympics.
"It was the hardest thing to get used to," she admitted. "I thought, 'Why do people judge me for the way I look?' It's not as if I was trying to be a model.
"I always had a bit of an insecurity about the way I looked growing up. I knew that I wasn't the most attractive girl at school.
"Even when I'd been on a night out, no boys would want to talk to me. So those comments hurt."
Rebecca – who won two gold medals at the 2008 Olympic Games and announced her retirement from competitive swimming in January 2013 – is currently engaged to boyfriend Harry Needs.
The happy couple announced their plans to wed last March after fellow swimmer Harry popped the question to his girlfriend of two years.