I think it is pathetic to have to go out of your way to label YOURSELF as a "black woman". FWIW I would think it similarly pathetic to label yourself as a white, an asian, an indian, or anything else in normal circumstances. Normal circumstances? I mean when the topic of conversation doesn't call specifically for identifying your right to expertise.
I've read that 4% of ALL Americans have at least some black heritage. So, on that basis, 96% of ALL Americans have as much right as Markle to be speaking up for "blacks". She is a very poor role-model/ convincing spokesperson for "black woman" and I think she diminishes herself, and her opinion, every time she tries to puff herself up with that. P.S., I have no doubt that both blacks and women face challenges I can't fully relate to, no matter how much I try. But it is exceptionally hard to take Markle as an good example of someone who had an exceptionally tough life.
Now, if she identified as "a spoiled, pompous brat" who somehow managed to turn off the Queen of England and much of the rest of England right quickly...well, maybe that would be something she could speak with some authority about.