Amanda Holden - who joined Simon Cowell and Piers Morgan on the judging panel for Susan's first audition - has spoken of her admiration for the rising star.
As Susan's debut album became the fastest-selling of all time last week, Amanda exclusively told HELLO!: "It's incredible, but to be honest I'm not at all surprised."
"She's phenomenal, and her story has gone worldwide, so of course her album sales would do the same."
But Susan has been making headlines with her personal behaviour, too. After briefly checking into a treatment clinic and photos of her sucking her thumb in America, the singer left onlookers wondering about her vulnerability.
Amanda, however, believes Susan is strong enough to handle the pressures of fame.
"You've got to remember her audition. She was feisty and strong, and funny and flirty - she's a really big character. She's had to deal with a lot in her life, she got through it and she's a stronger person for it, so we mustn't underestimate her strengths."
Amanda, pictured leading the Christmas singing at the Ferrero Rocher concert in London's Westfield mall last week, is keen to congratulate Susan in person.
"I think we will have a chance to catch up with her before Christmas," she says.
"She's been all over the world and none of us have been able to pin her down!"