This crown (though oversized in diameter) looks like it could be a headdress for Lady Crawley. The era of Downton Abbey saw the opening of Tutenhkamun's tomb in 1922, reviving Egyptomania and impacting the burgeoning Art Deco style. Unbelievably this piece is over 2000 years old and was worn around the mummy bandages of Pediamenopet (Petamenophis).
The Louvre is the home of this artifact and there is a discrepancy between their didactic text and the internet, but from what I can gather, Pediamenopet was a high priest and official serving multiple Pharaohs around the 25th and 26th dynasties (760-525 BC). His tomb (#33 in the Theban Necropolis) is massive, with multiple levels and 330 meters of corridors inscribed with important texts such as the Book of the Dead. His resting place is larger than many Pharaohs and this crown, evoking a myrtle wreath, is a symbol for a person of great social importance.
Myth has it that Pediamenopet was a renowned magician and left a curse. While exploring the tomb, both a French scholar in 1798, and a German archaeologist in 1874, fell down the 7 meter long shaft that leads to Pediamenopet's burial chamber. Recently an Egyptian archaeologist made the same fall but survived with considerable injury. The metal plate intended to cover the shaft seemed to have disappeared....
Reopening the tomb : http://www.touregypt.net/featurestories/petamenophis.htm