The way I see it is she was going for a certain character, she wasn't trying to do black inmate #7342 or an African tribal woman or anything of that ilk. It all matters based on the context...Ben Stiller in Zoolander, Robert Downey Jr. in Tropic Thunder, Rob in Always Sunny, those were funny, nothing really racist about them. It's not racist just because a white person paints themselves black. Now, in some situations it is racist because of the way "blackface" is used (eg. the traditional, overly exaggerated look), especially when it's just the face that was painted black, hence the term, "blackface". But when it's not just the face, but the whole body, and you're playing a specific character...Well that's not something to outrage about.
Of course, I don't think it's a very well-known character (generally, only people that have Netflix, and have seen OITNB, would get it), and the fact that it is a black character in a prison jumpsuit, without widespread context, was probably a poor choice.
To those who say intentions don't matter, that's the entire point of understanding one another. Understanding one's intentions rather than shoehorning in your own ideas about why someone did something and what it means.