Her action wasn't justified.The umpire wasn't being sexist.He endured plenty before finally giving the penalty game for the 'thief' insult.TBF,she may not have seen the coaching that sparked the initial warning,,but the guy was her employee and I think it is only fair that she be held responsible for his actions at least to that minor extent.Serena should have been prepared to accept that,but in her excited and frustrated state,she couldn't.
Djokovic thought that while Ramos pushed Serena too far,he wasn't being sexist.Navratilova said that it wasn't the right time to bring sexism up - which also implied that she didn't think Ramos was being sexist.Since both Djokovic and Navratilova are players,and Navratilova is a woman,you wouldn't expect them to be biased against Serena.So this to me is pretty firm confirmation that Ramos wasn't being sexist.Billie Jean King and the WTA have sided with Serena but are wrong on this one,IMHO.
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.