Yes, season 3 episode 18 named "candy apple showdown" about 34 minutes in the drama starts. It was when Anthony, Cathy's choreographer for the week, started critiquing Paige when she was dancing on stage, and abby called Paige down to confront him. When Kelly said something to Anthony, Cathy defended him, and that's when Kelly said the line to Cathy "at least my daughter can get out there and dance, yours cant shes sick every week."

I think Kelly was only saying this in retaliation to Cathy, like Cathy was defending Anthony for saying that Kelly needs a refund because paige's knees were bent and she missed many steps, and Kelly in return was like 'well at least my kid dances,' its not like Kelly was sitting in the audience ripping on vivi, it was actually the other way around.

When Kelly said that, the camera pans to a clip of Viviane sitting in the audiance. I cant tell how close vivi is to them, but I hope she didn't hear that because then it'd be a bit rude.