I read it as her explaining how this choice of phrase, done likely without any malice, carried with it additional and possibly unintended connotations to her, due to her past experiences.

Despite being well defined in dictionaries, language is, like everything else about the human experience, inherently subjective.

So no, I don't think she's providing a rule for you to follow - I think she's just letting the reader know how a small phrase can have an impact beyond its intent.

If the context hadn't been in front of a client, perhaps she would have been able to ask for clarification of what was meant - and the whole thing wouldn't have cause such a big, hidden reaction in her. The context made this more difficult that it should have been - it is not saying "don't ever say this or you're sexist", that is what you've read into it yourself.

Are you seriously arguing that there's a fundamental difference in the way the sexes harbour grudges? I think you're wrong there dude...

There's lots of guidelines about what not to do. There's less guidance about what to do instead.

I think personally I'd consider it a success just to be aware that whatever you're doing now might not be working, or might not work on this particular person - and with this in mind, look for feedback/signals and adjust your behaviour to circumstances.