Very old issue indeed! But we can't forget that Savoy Family members, during the Monarchy, hold the title of Prince(ss) of Savoy; only in 1948 those who were living in Italy had their official surname changed into "Savoy-place name of their title", but since this is a rule of the Republican Constitution it doesn't affect the titles.
So it correct saying that Emanuele Filiberto was Prince of Savoy, nobody can dispute it.
So what was Emanuele Filiberto’s correct style? HRH prince Emanuele Filiberto of Savoy, duke of Aosta? HRH Emanuele Filiberto, prince of Savoy, duke of Aosta? Were all the members of the IRF Royal Highnesses? Was there also a title of prince of Italy?
BTW, yes, she looks very regal, also in the video of her son Aimone’s wedding where you can see her gestures.
Is Princess Astrid of Belgium wearing her jewelry now ?
Well princess Astrid usually wear a tiara that was photopraphed already on a young duchess Anne of Aosta, but I don’t know if this tiara was already worn by Helene. Then, I’ve read elsewhere on the forum that Astrid worn another Aosta tiara in 1992 (the same tiara that her daughter in law Isabelle worn at her own wedding) and an Aosta emeralds necklace at king Harald 70 birthday. However since I wasn’t able to find any pics of these jewels I don’t know what jewels they are.
About Helene’s jewels I found this page,
http://www.angelfire.com/realm3/casasavoia/fifteen.html
There are here 2 tiaras, one emeralds necklace (possibly the same that Astrid worn) and some other jewels. One of the tiaras has a motif with Savoy knots and is very much similar but not identical to the one now owned by the duke of Aosta. Maybe it was modified, maybe there are two similar tiaras (this isn’t likely, is it?).
Here Helene with another tiara and another necklace,
File:Elenaaosta.jpg - Wikipedia
She seems to like very much that collier de chien necklace since she’s wearing it in all 3 pics! Lol
Finally I’m interested: where did she live mainly? In which year did she move to Naples? In which part of the Capodimonte royal palace did she live? Is it true that she could continue to live in the royal palace also after 1946? Did she and/or her daughter in law Anne owned some villa in Castellamare or on the Costiera? In which house did she die? There is a video of her funerals on youtube that show her carriage coming out of the Real Albergo Quisisana, maybe she used to live in that hotel?