It looks like a bird version of the Elizabethan collars that they put on dogs and cats after surgery.
It's a bib of sorts, made out of suede leather, because she's an unabashed feather-picker. The "bib" (which is really more like a cape, since it covers both front and back) slows her down, but it doesn't stop her feather-picking.
Some birds are destined to pick. I think she's one, especially since she's been doing it for +5 years now despite anything and everything I've tried.
The black strip around the top of the cape is a strip of velcro, which is additional security against her reaching down and ripping out more feathers. She hates that thing, but doesn't say much about it.