If I may point out the obvious, the only person here taking her joke seriously is you :).
At the same time, there are serious reasons, beyond Twain’s use of the n-word, to level the charge of “racism” against him; look, for example, at his writings about American Indians, starting with Injun Joe.
For me, I can think of a few female stand-up bits that have really impressed me: early Whoopi Goldberg bits were phenomenal, and Sarah Silverman’s bit on The Aristocrats was the funniest and most painful telling of the joke in the movie, and there are a few others. But then, I don’t find most stand-up all that entertaining, with the singular exception of Louis CK, who speaks to me in a way no other stand-up does.