It's not really professional nor good judgement for a commentator to say something like this about another player.
She may hate her but we don't need to know about that.
Wozniacki isn't the brightest bulb out there.
I believe the reason is that Ostapenko is not the ideal practice player. The way she plays her matches is the way she practices, she goes for the lines and does not give you any rythm. In practice players are looking to find their timing by hitting the ball back to each other more often. Ostapenko apparently doesn't do that. It's something that was talked about a few years ago where many players said they didn't like practicing with her.