The 51-year-old Irish warbler told the Metro that the Malvern teen made fun of her for being fat.
Mary told the paper: “She was being a little bit of a missy. People were talking about her thinness and she started talking about fat people.
“And, you know, I’m a big woman, which she got quite abrupt about, so I said to her, ‘You know, every one of us has something wrong with us, there’s none of us perfect and you can’t keep putting other people down because you’re feeling low. That’s bullying.’”
Luckily Cher, 17, apologised to Mary because she “realised she was wrong.”
The pair, who are currently performing together on the X Factor tour, have clearly kissed and made up as just last week Mary was singing the teen rapper’s praises in another interview.
She said: “Cher’s a completely different girl – she’s looking after herself now. She’s calmed down an awful lot.
“She still has her moments, but she’s a young kid. She wants to reach for the stars, she wants it all.”