Kate, whose husband Derek Draper remains in hospital after contracting Covid-19, recorded a message of support for the presenter.
Ranvir was shown the video after her first dance on Saturday’s semi-final.
Addressing the camera, Kate told her: “Ranvir? The semi-finals? This is unbelievable. It’s not though, is it? Because you are unbelievable.
“It’s just so fantastic watching you. You are amazing. We all know you are amazing and now the world knows it too.
“Hope you get to the final but whatever happens you are the absolute winner of this series.”
Ranvir responded: “We all know what she is going through. She typifies what everyone is going through this year and it’s so wonderful she found time to think of me. That is her all over.
“Thank you so much to her. It means so much for me.”
Derek Draper was placed in an induced coma after being admitted to hospital with coronavirus in March.
In October, Kate confirmed the former lobbyist and political adviser was able to breathe without a ventilator and had mouthed his first word.
The couple married in 2005 and have a daughter and a son.