This is crazy to me, I feel like this is a first step towards book banning. She was writing about her own life, which happened to be during a time of common racism. I don't feel like she was especially derogatory towards Natives, I think she was showing what most white people were really like. And for every time Ma was vocal about her hatred, Pa was equally vocal about his, respect isn't the word, but viewing them more equally than her. Now, the minstrel show is very racist, but it was common entertainment up until vaudeville, so not really shocking. She also very clearly credits Dr. Tann for saving them, and seemed to have some fond memories of him. His laugh, especially. People need to remember that she was writing about the 1860's, in the 1930's, and she seems pretty progressive for both of those times.
I had no problems understanding that the views weren't right anymore when I read these, neither did my daughter, and neither will my granddaughter. Just explain to your kids, but don't strip her of her honours.