Joan did go on to say about Martha being black but it was after mentioning that she was a woman. That was mentioned first, regardless of the emphasis. And I think that someone who is a nurse would know that that there were already women doctors, and had been for quite a few years. Some people get annoyed about the science or lack of in SF; I get annoyed when women's history is overlooked, and especially when attributed to a character who could be expected to be aware of it.