I don't think it will matter if the officer or whatever is black or white. Not sure it's an officer. Photos seem to show the shooter wearing a white dress shirt with cufflink. Could be a congresscritter, or many other other types of people. Since the person was armed, it could be an officer, but is not certain.
She broke through a window and started to climb through. It is not unreasonable to think she was a threat. Not real easy to tell she was female, the way she was dressed, either, from what little I saw in the video.
Castle doctrine is usually restricted to someone actually being inside your house. First, this isn’t Mr. Cufflink’s house. Second, she hadn’t breached the threshold.
There were cops all around her and Mr. Cufflink doesn’t appear to be a law officer. The big question is why was he carrying a weapon inside the Capitol?