I posted the picture to Google Images, and it says its Ileana of Romania. Maybe someone else can confirm that.
I know that the tiara in the following photo is not the famous grand tiara worn by the Luxembourg grand duchesses (Charlotte wore it at her wedding and abdication ceremonies, and gave it to her daughter-in-law). But I've seen this worn by Josephine-Charlotte and Maria Teresa. Is it in the grand ducal family? Or perhaps I'm confusing it with another tiara very like it?
Also, can anybody identify the royal wearing it? Here's the link (Pinterest doesn't always identify the people in its photos) --