TBF,I can see things from Serena's point of view.She's having a really hard final - desperately trying to find a way of coping with Osaka's game.Suddenly,the umpire gives her a warning.Why ? She's done nothing wrong.Like she really needed that - she's having enough problems already.So from Serena's point-of-view,the umpire was partially responsible for her smashing her racket,by picking on her when she hadn't done anything,which is why she called him a thief.
So I can sympathise with her right up until before the point where she accused Ramos of sexism - which wasn't justified.I agree with Novak Djokovic on that.
What I think the umpires and authorities should do,is warn players that coaching will be regarded as coaching even if the player may not have seen it. Because the officials cannot tell whether they saw it or not.