Thanks for your reply Beth, it's always a pleasure to read your comments. Well, now there are two of us thinking about the possibility I raised. When observing the necklace I always found strange how it could be converted into a tiara. Besides there are two other thinks that made me think:
1. observing the necklace we can see that there are many things "happening" behind the central motif; 2. The center of the necklace appears to be at a different level of the rest of the necklace. Contrary to the usual necklaces this one does not seem to be "flat".