Emma, who will present the BBC One talent show with Marvin Humes in January, will speak about the brand new fourth series on Alan Carr: Chatty Man Christmas Special.
Emma said: "Rita is doing absolutely brilliantly. We've filmed everything up until the Knockouts, so I've seen her in full flow and she's just… you can't imagine trying to replace Kylie, and being the person who sits in that chair after her, you would imagine has a very big job on their hands, and Rita's done it seamlessly, and really well.
"She said she was really nervous beforehand, but she just went in there, sat in the chair, and she was off and running."
Emma, who continued to say that the "talent is phenomenal" this year, isn't the only person to praise Rita.
Earlier this month, Marvin told Reveal that Rita was doing a "great job" in her new role.
"Rita's wicked," Marvin told us. "She's taken to it instantly. Since the first day she started, it's like she's been in the chair for years.
"I'm looking forward to everyone seeing a different side to her. She's doing a great job."
The Voice UK will return on Saturday 10 January 2015 on BBC One.
Guests on the two-hour Chatty Man Christmas Special are: Phillip Schofield, Dan Stevens, Sarah Millican, Terry Wogan, Gino DeCampo, Emma Willis, Sam Smith and McBusted. The show airs at 9pm on Channel 4 on 25 December.
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Watch the new trailer for The Voice UK below: