The headdress she's wearing does actually apply to her cultural background. Google "Trinidad headdress". They use peacock feathers, while Native Americans don't. It's been a common misconception because not many people these days know of aboriginal people outside of Native American and Inuit. Showing her culture in her releases isn't the same as a 100% Caucasian/European wearing a headdress to a party.
I concede that you have a valid point, and after reading a bit more, I understand that it may have been Nicki Minaj’s intention to wear a less flamboyant version of the Trinidad carnival headdress. (On the other hand, the assertion about the “tubes” as proof of its non-appropriative-ness sounds like bullshit to me.) However, I believe that the designer is less innocent, because a quick look at the designer’s other material makes it painfully obvious that the designer specialises in “bohemian” fashion with lots of feathers and leather fringes. At least the maker was thinking along the lines of hippie/hipster native headdress.
I’m not here to hate Nicki Minaj. All that I’m saying is that I believe that she should take a second look at what the poster speaks to the public.
I might also note that the designer dissed Nicki before, saying, “I would never dress Nicki Minaj, she has no talent, no style, and no class,” so all the more reason Nicki shouldn’t wear that one.