That's cool, but this it isn't a "sentiment." It's a simple fact: our choices carry consequences. We decide if we'll accept those consequences or not. To say that other people have decided it for us by providing those consequences puts the responsibility for our choice on them, not on us.
Is that where it belongs?
I don't generally use the word in question, the "n-word," for my own reasons. I am making that choice. No one is making it for me, and no one can allow me or not allow me to use the word. If I were to maintain that, I would be stating clearly that I willingly let others manipulate me, and all I know to do about it is feebly object on an internet forum.
Now, if I do choose to use it, I am also choosing to accept any repercussions for it. I can't expect to use it and not face objections, since I know it's considered an objectionable word.
And that's what's really being said by some who holler about "not being allowed" to use it: "I not only want to be able to say it, but to say it without facing any penalty or censure." Um, well, no. That's not part of the deal, sorry. It's a crap little word, with a ton of negative baggage, and you can't use it without toting some of that baggage along. Even the people who do use it are aware of that.
Again, though, that's not what I'm addressing. I'm talking about who chooses for you what you can say and what you can't? And I'm making the argument that even in the face of possible repercussions, even in the face of an outright threat of harm, it is still you who makes this choice.
This relates to the OP in a direct way: the sentiment, "it's okay, I can speak poorly of them, because I'm one of them," is an attempt to defer the consequences of objectionable opinions by "in-grouping." I'd call it fallacious, though I'm not really sure of the type.
But her reasoning is likely something to the effect that criticism of a group should come only from within the group, because only the members of the group really understand the dynamics. Outsiders do not and cannot understand, and so their criticism is often perceived as bigoted or racist, by that very virtue.
I do feel what the girl in the OP said was a fallacy. I just don't know how to articulate my reasons.