It seems like the Princess Ileana wore the brooch at the Wedding of her son, Archduke Stefan of Austria, in 1954. She also looks to be wearing her ruby earrings, which I recall her mentioning in her auto-biography.

Princess Ileana only sold the Vladimir Sapphire Tiara in the 1950s, but the family managed to retain most of her other jewels until much later. (the diamond tiara may still belong to them and a big sapphire pendant was only sold in 1980). This it is likely that the Brooch may still belong to them as it has not publicly appeared for sale, and we also don't have many pictures of her children and grandchildren.