The MK1 member revealed that she has had a girlfriend for the past year.
"If I go out and guys come up to me they look really confused when I say I've got a girlfriend," she told The Sun.
"It's weird because all the girls think I'm a gay and all the guys think I'm straight.
"But I actually like boys and girls, so I get the best of both worlds."
Talking about her current relationship, she said: "I went from having a boyfriend to a girlfriend and it was really funny.
"I was friends with this girl in my town and we used to hang out and then one day I started feeling a bit different and I thought, 'I like both'."
With Jade Ellis and Lucy Spraggan both confirming they are lesbians, Ella Henderson is the only straight female in the competition.
Rundle said that she is not attracted to either of her rivals, saying: "They haven't given me the eye either. They've got their own people.
"And Jade is like my best friend. We have such a laugh together. And, to be honest, if I go out I tend to look at guys first."
She added: "But I'm not into any of the guys on the show. They're all a bit young for me."
The 19-year-old recently appeared topless in a pre-X Factor photo.
Watch MK1 talk to Digital Spy below: