This is such a strange argument you're making here. I am entirely comfortable with who I am. More than that, I am very fortunate to be actively happy about the person I am. There are facets of me I'd change, but they're relatively limited. I'm not arguing because I feel if I defend this woman, I can follow in her footsteps. I also have no particular dispensation towards to white people. I don't care about white people specifically any more than I care about any other people. I specifically don't have any reason to care about Rachel Dolezal, a woman who I've never met and probably have very little in common in.
The reason I care, is because if she's not pretending, and she wakes up in the morning and looks in the mirror and sees a skin that isn't hers and thinks, "that's wrong/that's not me/that's not who I am"; and she finds a body she's comfortable living in, and other people tell her that's wrong and try to force her into a body she's not comfortable in and into being a person she isn't, then there is something *wrong* going on, and someone is being hurt.
Of course, if, deep down, she hates pretending to be black and only does it for the NAACP salary, is or ambivalent and does it for attention, then you're right entirely - it' deeply offensive and she is wrong. But, assuming for the time being that's not why she does it, I have reason to care.