Of course, this is Mary at her brattiest. Surely, the wise Martha will correct her, and Mary's racism will be just another part of the person she will leave behind as her face becomes less punchable.
Nope! Unlike Mark Twain's controversial Huck Finn, where the racially insensitive language is offset by Huck and Jim's tender, buddy cop dynamic, Mary's virulent racism is never corrected by anyone or by anything that happens in the book. In fact, Martha uses her role as the voice of reason in the situation to blame Mary's awful behavior on the fact that she is from India, where there are "a lot of blacks there instead of respectable white people."
"You have to clap your hands three times to make sure they're not hiding in the shadows."
Though it's the last time that black people are explicitly referenced, there's also a strong undercurrent of symbolic racism. For instance, Mary can't begin her journey to self-discovery until Martha changes her out of her black clothes and puts on white clothes, while Mary makes the very odd statement that she hates everything black.
Again, this statement isn't even addressed. Once she changes into white clothing and no longer has to deal with the "black" Indian servants Martha blames for her poor character, Mary heads out into the mansion and begins her journey of discovery.
"Good news, I found a rope! For ... skipping."