You can't claim to be black when you're white. You can't claim to be white when you're black. The difference is obvious. It's colour. You can love and identify with culture that comes from being whatever colour you want, but it doesn't make you it!
I've never, nor do I know anyone that has, wondered if their inner thoughts and feeling are black, or white. That's why you can't be transracial. Because it's not about something you can change or have been born wrong into. You don't think black or think white, you just think.
You don't get to put "white" on any paperwork identifying you when you are black because it's not true, it's your appearance, it's not a feeling inside. Unlike, I imagine, trans men and women, where it is a feeling/thoughts inside. That is why they're different things.
RD can say all she likes that she identifies with black culture and wants to be a part of it but she isn't and never will be actually black. She's just ridiculous.