I don't find what she did ignorant at all. I also don't take the view that people should never be able to dress up as a black character. Such thoughts are ethnnocentric and defeatist. One guy argued that intent isn't pertinent. Bullshit.
There's a full mile away from this:

A girl who, from what I'm seeing here, fully appreciates the character and wanted to represent her for Halloween, in a respectful manner.
And this:

Lumping the two and being offended at both is asinine and reeks of trying to be offended for the sake of offense.
Frankly, it's hard to take any other position. If they want to talk civilly, fine. But tell them to leave their ethnocentrism at the door.