The more I hear the more I blame H rather than M for this car crash drama.
Yes I can imagine she was abrasive and maybe rude in her assertive go getting I'm going to be a huge success type mentality, and it rubbed the firm up the wrong way.
Staff started to use the word bully, W started shouting.
Harry should have discussed it with M & said:
Look, I think you're amazing I love your drive, but round here we can't do that brusque ordering staff around thing, we have to try to look all magnanimous and grateful, or it looks bad.
I reckon MM, actress that she is, would then have gone into full gracious Duchess mode.
I think he didn't tell her how to play it.
I think H because of all his baggage about being the spare couldn't tolerate any criticism of the women he'd chosen, so couldn't deal with it rationally and ended up in the dogs bowl.