The 'Fashion Police' host flew out to Las Vegas, where Sharon was filming 'America's Got Talent', to surprise her on the special day - which takes place annually on the second Sunday of every May in the US - and organised the musical tribute to take place during a break in shooting.
Speaking in her Closer magazine column, Kelly said: "I flew with my mum to Las Vegas last week, as she was working on 'America's Got Talent', and I spent the Saturday organising her Mother's Day surprises. I put up 300 balloons in her hotel room and got a Liza Minnelli impersonator to sing her a song during the break!"
But the 26-year-old star didn't only spoil her mother while she was in Las Vegas - she also made sure she enjoyed herself too.
Kelly joined David Arquette and Jeff Beacher - who she works with at Beacher's Madhouse, a variety theatre in Los Angeles - for a night out at the Yellowtail club, where they staged their own impromptu dance competition.
She revealed: "On the Saturday night, when my mum was working, I went out to the Yellowtail club with my Madhouse comedy show partners David and Jeff, which was fun. None of us really drink, especially David, who has never looked better or happier. So the three of us had a little dance competition to see who could do the most absurd dance moves and I'm pretty sure David won - but only by a little."
David spent four weeks at the Betty Ford Center to be treated for alcoholism following his separation from his wife Courteney Cox - with whom he has a six-year-old daughter Coco - and has been sober since he checked out at the end of January.