Racism accusations apart - I have feeling that Meghan was not prepared for the tight-assed protocol that surrounds life in the palace. I think she thought that being a princess would be great and that it would give her the options of espousing some of her topics - such as womens rights.
I do not believe that she liked to follow the "rules" and that alone would have earned her negative reactions at the palace.
People may think that the Royals lead a privileged life, but my understanding of their life is that it is ruled by duties they are expected to perform, and rules of conduct - including dress, makeup and hair - that they are expected to follow.
Diana didn't like it and flouted those rules. I feel that Meghan hated the restrictions on her liberty and made herself unpopular by constantly fighting against these rules.
I feel that it did not help that she was an actress nor that she was of mixed race. I do not believe a lot of what she has alleged.