I don't read this as her telling you you're "not allowed" to say something.

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.