And do you only wear a tiara if you are royal, or titled? If Melania wanted to wear one, could she have done?
American women don't wear tiaras as a rule (except maybe with a wedding veil) and I think those tend to be fake jewels. I guarantee that there would have been a huge outcry in the States if she had worn one (does she think she's royal, etc.). Years ago Jackie Kennedy wore some diamond clips in her hair that had a kind of tiara effect (I think it was to a state dinner in France) and she was criticized in the US for that (Queen Jackie, etc).
I found a picture. It was a dinner at Versailles