Pergel feels Kato is acting unfairly?
Yes that's the accusation at least.
I only caught a few things briefly because I also wanted to watch the Harimoto game.
The drama seemed to happen in game 4 (and the effects carried into the last fifth game).
We'll have to rewatch later if we want more clarity, but in the brief conversation of Pergel, her coach and the ref after game 4, Pergel specifically mentioned "cheating" in regards to Kato's serve.
I would suspect that it was about the usual hidden serves at worst. Probably because the umpire didn't call it/them (but Pergel perceived it/them as illegal) and the emotions were raw (especially fer Pergel since she's playing in front of her home crowd) things became more dramatic as needed be.
That's just me guessing though. We'll have to look back at it later if we want to know for sure.