The singer, who made it to the final of Strictly Come Dancing, said Cole's relationship with the American was "real".
She told Jonathan Ross: "She's known him for quite a long time. A few years ago, he danced for her the first time.
"Yeah he's a lovely guy so I'm happy that he makes her happy. I think it could definitely go the distance, yeah they're really happy."
But she said any marriage plans of her own to long-term boyfriend Justin Scott had been put on hold because she was so busy, telling Ross: "It's just something that we've not really got round to doing."
And she said rumours of romance between Strictly contestants were wide of the mark.
"I think it was the first year that there's been no affairs backstage; I think everyone was really disappointed.
"It is a really intimate situation, you're spending six/seven hours a day and it's quite physical but yeah, nothing happened this year."
Walsh was joined on Ross's ITV chat show by comic Jo Brand and Les Miserables star Eddie Redmayne.