And yeah, you'd think that if they did it with Carter/Katar they'd do it with Kendra/Shayera.
They initially did it during Zero Hour, with the whole Hawk Avatar angle that nobody particularly liked. In that version, Hawkworld Katar merged with Carter, Shiera and every other Hawk-themed DC character ever.
Then, when Geoff brought him back, he linked both the Golden Age and Silver Age versions by explaining that the Nth Metal came from a crashed Thanagarian soulship discovered by Khufu & Chay-Ara in ancient Egypt. This time, however, Carter was the dominant personality, instead of the Hawkworld Katar. Smart idea, given that Carter and Silver Age Katar were previously smooshed into the same guy thanks to Hawkworld.