If you look back over Kate Middleton's eight-year run in the royal family, you'll notice a pattern to her tiara appearances. Aside from her wedding—where she wore the Cartier Scroll Tiara—Kate has only ever worn tiaras to either diplomatic receptions or state visits of European royalty.
All of her non-wedding tiara appearances have been at Buckingham Palace.
So it seems there is something of a 'new rule' in place for tiaras—it must be for an event big enough (see above for examples) and it must be in England (you have to assume travelling with a priceless tiara overseas is a nightmare).
And since Meghan hasn't attended any diplomatic receptions or state visits at Buckingham Palace, it seems logical that she hasn't worn a tiara.
Meghan has attended two state dinners in both Tonga and Fiji, but it looks as if neither event was enough to warrant some diamond headwear.
For her state dinner in Fiji, The Sun reported that Meghan enquired about wearing a tiara but her father-in-law, Prince Charles, warned her against it.
"Meghan did not understand all of this because she was new to the role and so Prince Charles told her that it would not be appropriate. It was very kindly done," read the report.
(It's also worth noting here that Kate has attended overseas state dinners in Norway, France, India and Sweden and has always chosen to skip a tiara, likely for the same reason.)
Just like the monarchy, tiara etiquette has come a long way in the past ten to twenty years. Back when Princess Margaret was the young royal about town, tiaras made appearances at everything from birthday parties to theatre shows.
Nowadays, things are much different.
Since the monarchy is on a mission to modernise and seem more 'down to earth,' wearing a tiara worth hundreds of thousands (if not millions) of dollars to any old event doesn't quite match the theme.
And since Meghan herself has always courted a more unpretentious and contemporary approach to being a royal, it's no surprise she's opted to skip the pomp where she can.
Meghan might be in the public eye just as much as her sister-in-law, but when it comes to the monarchy, she's lower in rank.
William and Kate are set to become the King and Queen of England in the not-so-distant future, so there is always going to be more occasions for them to wine and dine with other heads of state and monarchs, where Harry and Meghan are lower ranked and are more likely to take the smaller, more intimate engagements.
Nonetheless, we're hoping that Meghan does get a chance to wear a tiara in the future, because when you look this good in one, it's practically criminal not to.